2020 New Year–Advent of Shiramochi-ō (2020正月-白餅王降臨-) is a holiday event that occurred in the Great Tomb of Nazarick. It was released on December 30, 2019 to January 9, 2020. The event was re-released on December 28, 2020 to January 15, 2021.
Momonga visits the Round Table Room for a meeting and finds Albedo and Demiurge relaxing by a kotatsu and is confused. When he looks at it closely, a mysterious New Year mood has spread in Nazarick. Momonga set out to restore Nazarick.
Demiurge and his Evil Lords were conducting an investigation of the ruined Throne Room trying to make sense of the Crack on where the Throne of Kings once stood. Demiurge ponders why the Crack on the 10th Floor is the only anomaly that allows them to summon Chaos Beasts. Evil Lord Greed suggests that perhaps the difference lies with where the Crack stands, the former site of where the Throne of Kings. Demiurge feels that could be possible though it is still too early to tell. More importantly this mystery must be solved in order to keep Nazarick safe and return Momonga's place upon the throne of Nazarick. Suddenly the Crack beings to glow despite the fact that the scheduled Chaos Beast cycle isn't until later. Demiurge deduces that something is being summoned and sure enough, a strange monster resembling a Kagami mochi appears.
The demons are unsure if it is a Chaos Beast. Just to be safe Demiurge tries to use his mental magic, [Command Mantra], on it. However to the demons' shock it is immune to his spell. The Floor Guardian deduces that the creature is a summon and under the control of a powerful Summoner. Despite wanting to capture it for study, he realizes it is a dangerous entity and orders his demons to destroy the threat in Nazarick, which proves tricky as the monster is not an easy foe to defeat with. When Evil Lord Wrath strikes a blow to the monster it begins to glow and the entire room in engulfed in white light.
Momonga, who is visiting the Round Table Room for a meeting, finds Albedo and Demiurge hanging there eating mandarin oranges and warming their feet under a Roundtable that has been converted into a kotatsu. Even more confusing Albedo is wearing a kimono. Albedo seeing him present greets him and says "Happy New Year", promising to continue to work hard and make constant efforts for the sake of his supreme self. Momonga is stunned by the revelation that it is already New Year's and that the Overseer Guardian is aware of such a holiday. Momonga decides to get back to the purpose of the meeting but is shocked when Albedo and Demiurge move in favor to skip the meeting and enjoy the holiday. Now worried, Momonga sees that the two are acting out of character. He first confirms that the mandarin oranges are real and not an illusion. This leads him to the conclusion that some sort of mental effect is affecting both Floor Guardians. So far it seems that they are not hostile and don't appear to be completely under someone's control, making him more curious as why they are celebrating New Year's. Having too little information and needing more answers, Momonga decides to check on other parts of Nazarick. For the time being, he chooses to leave Albedo and Demiurge where they are as even though they are suffering from the mental effects of the enemy, it would not a good idea to stimulate them poorly and receive a counterattack. Playing along for now, Momonga allows the two to enjoy themselves noting that the two have been hard at work ever since the collapse of Nazarick. The two thank him of his generosity, promising to work harder next year.
Out in the corridor of the 9th Floor, Momonga resolves to investigate and discovers what is going on. He summons several Death Knights and Skeletons to search for any clues to the source of this New Year's mood on each floor. After he summons leave to do their investigations, Momonga then heads to the 1st Floor to check on things himself and contact Shalltear Bloodfallen. The vampire greets him, wishing him a Happy New Year, proving that she too is affected by whatever is spreading in Nazarick. From her he learns that she is heading to the 6th Floor for a patrol of the Crack in that location. It also seems to Momonga that Shalltear's influence of the New Year's mood is minor as she seems to be dedicated to doing her job unlike the two other Guardians he encountered. He deduces that this could be due to Shalltear being an undead and thus the mental effect is minor. If that's the case, that could explain why he himself was not affected. But the seriousness of the situation is foreboding despite the seeminly harmless antics of the ones under the New Year's spell, Momonga cannot rule out the possibility of an attack.
Momonga's silence worries Shalltear, but he quickly responds telling her it is nothing and offers to accompany her to the 6th Floor on her patrol. Shalltear is more than happy to accept the offer as it is a New Year's surprise to her. Upon arriving on the 6th Floor, they find the Mare Bello Fiore and Aura Bella Fiora dressed in New Year kimonos playing Hanetsuki with paddles and a Hane. The two elves greet the visitors to their floor. Momonga watching them play is happy to see them enjoying themselves like children, a sight which he thinks would make Bukubukuchagama happy. He then notices the kimonos they two are wearing and inquires where they received them. The twins state that the Homunculus Maids prepared them. In comparison to the mental effect of the twins, Momonga can say that mental obstruction is still occurring but the effect seems to be less than that of the Albedo's, but it is not as low as Shalltear. At this time Aura asks Shalltear if she wants to play, but Shalltear declines snobbishly stating that she does not want to act like a child and that she is on duty.
Though everything seems okay, the Crack soon activates pouring out more miasma than usual and popping out a new monster that resembles a kadomatsu. Seeing the new monster Shalltear tells her lord not to worry as she will deal with the new enemy. Momonga nevertheless asks Shalltear to allow him to fight with her against this new foe. The two alongside their undead troops then attack killing the kadomatsu monster. Momonga seeing that it was a weak monster is disappointed. Easily dispatching them with the help of the Floor Guardians, Momonga wonders what type of monster the kadomatsu was. However when Shalltear is unable to recognize the monster anything but a Chaos Beast, not even noticing its appearance as a kadomats. Thinking it over Momonga notes that usually, Chaotic Beasts appear from Crack, but this time, some entities appear as if they were being summoned via by special skills from the miasma. This pattern strangely resembles a Chaos Zone that occasionally occurs outside the dungeon. This does not sit well with Momonga, as Nazarick still contains Cracks and if a Chaos Zone has occurred within it could mean that other such phenomenon may happen. Worse the fact that Shalltear is mentally impaired, it may lead to a series of problems.
A Death Knight comes to report that the protagonist and his allies have returned to Nazarick and are on the 1st Floor. The Overlord thinking that those who were outside Nazarick at the time of this phenomenon, believes they may not be affected. Momonga decides to go back to the 1st Floor to welcome the protagonist, and tells Shalltear to resume her patrol duties and for the dark elf twins to continue on playing to their heart's content.
On the 1st Floor Momonga greets the protagonist, Slimeko and Solution Epsilon. Momonga nearly loses composure when Slimeko wishes him a Happy New Year as it shatters his belief that the New Year phenomena is the only endemic to the tomb. The protagonist explains that not to be the case as it seems only that the strange New Year's mood was settling only in Nazarick. The homunculus further details that his party passed by the Pleiades and Cocytus who wished them a "Happy New Year". In addition the protagonist confesses that he was already aware of the New Year holiday due to his reading in Ashurbanipal. Still he also finds it to be odd that others in Nazarick know about it as well. However he and his group played along until they could get what was going on in Nazarick. His shrewd thinking seems reasonably as Momonga admits that Nazarick is now in a state of emergency due to this phenomena where the entire staff of Nazarik has some kind of mental effect. As a result, everyone seems to be in a state close to "New Year's mood".
In addition there was an outbreak of a mysterious Chaos Beast, and while it seems insignificant everyone except them is mentally impaired. The three returned agents see the dire state Nazarick is in. Solution chastises herself for not acting when she noticed Yuri Alpha's behavior, but Momonga tells her that there was nothing she could have done. If she did it may have led to an unfortunate battle. Instead they could be thankful that they were outside of Nazarick when this situation happened. Since its confirmed that only those in Nazarick have been affected, other field agents like Sebas Tian might still be fine and sane. The protagonist suggest to his master that he recall the butler. As he told them both Shalltear and Albedo have been comprised by whatever is affecting Nazarick. Bringing back Sebas Tian should be enough to protect Nazarick for the time being at least until they get things under control. Momonga agrees and orders the three to send out a message to all their forces to be informed of the situation and be recalled.
After awhile Momonga receives a report from his undead forces surveying the floors that everyone has been accounted for save for Cocytus and the Pleiades who have left Nazarick. The protagonist having passed by Cocytus, recalls that the Floor Guardian mentioned about visiting a shrine. Momonga is confused about the mention of a shrine, and the protagonist clarifies that the maids and Floor Guardian were heading towards the Fake Nazarick. Momonga seeing that to be their destination then tells the protagonist and his allies to follow him there. To ensure Nazarick's protection, he leaves a [Message] to Shalltear to guard the 1st Floor while he is away.
Sure enough a strange tori is found on the 1st Floor of the Fake Nazraick. It is determined to be a Hatsumōde and usually appears at an entrance for a shrine. The protagonist surmises that Fake Nazarick may have been converted into one. Momonga recalls their previous conversation on the awareness of New Year's——in that few people in Nazarick should any knowledge of the New Year, save for the protagonist. Momonga though is an exception as he was aware of all the New Year's traditions. He surmises that the information is a by-product of the phenomenon that causes "New Year's mood". Slimeko inquires if Yuri who passed through the Hatsumōde knew what it was. Momonga is not sure but it could be so as whatever affected Nazarick has now affected its replica.
To make sure that the Hatsumōde is safe, Momonga sends forth a undead unit to cross the threshold. The skeleton vanish as soon as they pass the Hatsumōde, making Momonga deduce that there is another space on the other side. And after bringing skeletons back Momonga confirms that it is safe and the danger of being trapped is not zero. But as long as there is no other clue to restore the current situation of Nazarick, Momonga warns them that they should be aware of some danger. At worst, he tells his allies to consider escaping using a "Transition Gate". While in this world, the location of the transfer destination shifts, they should only use it in a really worst case emergency. Solution understand such procedures and tries to tell Momonga not to worry and to allow them to ensure his safety.
The protagonist's attention is directed to three mysterious shadowy figures being casted from the center of the entrance. Momonga sees that they are "Shadows" and from what he read in the protagonist's report they only appear in a Chaos Zone. They deduce that this Hatsumōde could juts be that or another kind of special area created by a Crack. Momonga muses that the Cracks are still a mystery no matter how much he investigates them. Undeterred Momonga leads his allies and advanced into the swarm of Shadows.
Momonga and his allies finally cross into the entrance and find that the interior of the fake dungeon has been radically changed. Instead of a perfect replica of Nazarick, they are faced with a desolate misty desert. Momonga wonders if the ones who came into Fake Nazarick did this, though the protagonists thinks it's more likely an enemy converted the area. To Momonga the only effect that can do something like this would be a high tier spell of [Creation] or [Change The World]. They are still in unknown territory, but there should be the danger of Chaos Beasts and Shadows. Other than that it's still a mystery, and Momonga proceeds to lead the NPCs and skeletons deeper into the area. He leaves the advance reconnaissance to Solution but warns her to be careful as there could be summons who have been mentally influenced. While Momonga hopes that they will be lax like Albedo, he can't be too sure. In addition they may have to expect a fight with Cocytus and the Pleiades. Slimeko is in awe at Momonga's assertiveness in this situation. Momonga continues to warns Solution to be wary of any traps that might appear and to use her Rogue class to disarm any that she might encounter.
While Solution scouts ahead, the protagonist advises that perhaps Momonga should remain behind in proper Nazarick, while he and the other continue on, as there are too many unclear points about the enemy's strength. Momonga disagrees, as the enemy may not always stay still, there next move may lead to the fall of Nazarick. Thus right now they should gather information quickly and hit the enemy as soon as possible. For that reason, Momonga reminds the homunculus that he should be prepared for some danger to prevent the worst outcome. Momonga is prepared to throw away as many undead troops as needed and has prepared multiple emergency escape means. The protagonist apologizes if he stepped out of his bounds, offering himself to be used as a shield if the situation calls for it. Slimeko also makes this same offer as well. Momonga is appreciative towards the gesture but states it should only be used as a last resort.
Suddenly Shadows appear, causing Momonga to pause in order to deal with them quickly so as to conserve his strength. Solution eventually returns and rpeorts that she has found Entoma Vasilissa Zeta who is baking New Year's confections by herself. So far it look like it appears to be safe and/ But they are unsure if Entoma is compromised so the group decides to greet her. Entoma welcomes them and explains that she was making mochi, which Momonga finds odd as she is not supposed to have a Cook class and surmises that the phenomena is responsible for giving her the skill.
The party and Momonga believe it to be best to pass through the area quickly but soon encounter a Mochi Type Beast. After killing it to their surprise it leaves behind mochi similar to a drop item. Entoma unperturbed at how they defeated the Chaos Beasts thanks them and asks if they can collect more mochi for her to bake. Momonga decides to play along with the charade and complies as does his allies as they collect the mochi by killing the nearby mochi monsters. Once they are done Entoma offers them green mochi, made from the mochi they collected and her green bread. While Slimeko is eager for the treat, Momonga and the protagonist advise her not to eat it, unsure of the effects of eating food in the strange area. Not to be rude to Entoma, Momonga asks her to doggy-bag it for them and they make their way to the next floor.
The the party approaches the 4th Floor of Fake Nazarick, which was originally an underground lake replica of the original but now has been changed to the strange misty world that surrounds them. Momonga though believes that the dungeon will return to its proper form once the cause is defeated. Still the remaking of the entire fake dungeon concerns him, after all, he still cannot wrap his mind of how this area was formed. Slimeko warns the group of approaching Shadows which annoys Momonga as he wants to avoid fighting needless battles and goes to engage them.
Later after dispatching the Shadows, Momonga notes that each floor can be accessed by a torri gate, which act as transfer gates. If that is so then there should be a transfer gate somewhere on the 4th Floor to the 5th Floor. Solution offers to scout ahead but, Slmeko hears a sound similar to a gunshot the party follows it deeper into the misty dimension. Solution scouts ahead only to return to report that she found CZ2I28 Delta acting odd in that she shooting a metal plate in the air. Momonga is left confused and decides to see for himself. He goes with the others and finds Shizu is doing as Solution reported.
Momonga asks if she is targeting at an enemy only for the Automaton to state she is "playing with the wind" and continues to shoot in the distance as it's fun. He later realizes that she is partaking in "kite flying", though Shizu's activity seems to be a bit off from what is actually done. Still when he hears that she is having fun he finds it acceptable even though she is under the "New Year's mood". Before the group departs they see a Kadomatsu Type Beast in the distance. Momonga not wishing to waste time thinks that it would be better to leave it alone. However the monster unexpectedly flies using a small blast of fire and goes into the air. The thing is heading towards Shizu's kite, and forces Momonga to take action. Momonga directs his Skeleton Archers to shoot the monster down, despite the protagonist's reservations, and kill it. Momonga insists on eliminating it and others as they could be a problem if there were enemy unit in the air. After all the Kadomatus Type Beasts are eliminated, Shizu thanks them and Momonga allows her to continue playing with her kite. Saying their goodbyes to Shizu the group head to the next transfer gate.
The party cross from the 5th and 6th Floors and reach the 7th Floor. While traveling Momonga explains that both floors' field effects have been modified cosmetically but their defenses for repelling intruders have remained the same. Oddly the traps are no longer active, probably because it is under the influence of mental effect, or because the dungeon does not register it as an invasion from the outside. Form what he can tell this phenomenon is closer to the feeling the dungeon being "overwritten" rather than re-developed. The protagonist agrees as the dungeon's traps are still good, but it can be inferred that there are some conditions on targets and range after being "overwritten". He theorizes that this could be why the true Great Tomb of Nazraick was not "overwritten" as maybe the structure was so complicated that the conditions for "overwriting" it could not be achieved.
While Momonga is thankful that the real dungeon was not physically affected, the re-writing of Fake Nazarick is still a threat. Slimeko admits whoever this enemy is, it is terrify if it can do such a thing. Momonga is not too sure if this is an enemy, but believes that this still to be just a phenomenon. To explain his view, Momonga asks the protagonist what he felt ever since he crossed into the Fake Nazarick. The protagonist replies that the experience has been strange yet if was too odd to be a trap and that there was a vague pattern. Their experience with Entoma and Shizu, a the Chaos Beasts appearing and attacking that is. Mysterious phenomena and actions were occurring, such as when they defeated the Chaos Beasts and the defeated monsters became drop items and attacking the air when there really was no need.
Originally he thought it was all some sort of elaborate trap but so far none of it seemed malicious. Momonga sees that he is not the only one who thinks of these instances. It's true that there were certain instances when a Chaos Beast appeared and attacked, but ——the attacks were too lukewarm for the purpose of eliminating intruders. Truth be told the attacks could have been more effective using better traps. Slimeko wonders aloud why are they encountering these situations and why are they not being taken seriously? The Overlord then proposes an idea that what if the main purpose of these attacks were not to repel intruders or destroy them?
For example, what if they were taking actions to fulfill the set conditions, such as a Chaos Beast would appear, and if you don't defeat it, you can't move on. Solution asks if the transfer gate will not work unless they finish a task? Momonga states that so far on each floor the gates were working without problems, but it may be because they met the "conditions". At the time with Entoma, she was baking a certain number of mochi. And at the time with Shizu, was trying to fly her kite. What if the torii only activates if that condition is met——Slimeko realizes that Momonga helped Shizu protect her kite because he realized the connection to the tasks and the gates. The protagonist so follows Momonga's thinking understanding that the maids they encountered had tasks that nedeed assistance and that they were supposed to complete them before moving unto the next floor. Momonga likens this whole event as a "quest". Shadows soon interrupted the party forcing them to take defensive action. Slimeko asks if that the Shadows are part of the tasks, which Momonga states to be no as he believed that those impaired by the mental effect act as givers of a quest. While these Shadows only target the receivers of the quest, almost like POP NPCs.
Later once defeating the Shadows, Momonga leads the group forward. Noticing Slimeko being quiet, he asks the slime what is wrong. Slimeko just states that she was still being awed by Momonga's leadership, leading them into an unknown land and still managing to maintain his compsure. Momonga laughs at this and elaborates that he was originally, used to capturing dungeons with his friends from Ainz Ooal Gown. Even though he doesn't know what kind of enemies and traps are in a dungeon, normally he would carefully conduct a preliminary survey, rush in several times, and devise measures to ensure that he can overcome. The Great Tomb of Nazarick was once an enemy territory until it was claimed by his guild. It was dangerous and difficult, but the joy at that time was beyond description.
As for this phenomenon it is a crisis for Nazarick, but when he is doing this, it makes him remember the old days and miss it. In fact he tells the party that, every time he reads their report, he becomes jealous. This confession shocks Slimeko, as she listens to her master tells them that he misses going off and departing into the unknown world and exploring. Knowing something he doesn't know, and sometimes encountering hardships, working with friends to overcome them, and feeling the real thrill of adventure.
The protagonist knows exactly how he feels, and that the task of exploring the outside world and the joy of overcoming difficulties and achieving something was something he had never felt before. Momonga confesses that if Nazarick had not collapsed he might have been the one, not the protagonist, who would be out. No that he dwells on it, adventure was my air and peace. No matter how hard it was, Momonga could endure it if he thought he could go around the world with his friends. But now this little adventure for him is entertaining, but there is no reason to give priority to having fun. The main purpose is to recover the situation in Nazarick. Momonga is content that afterwards that the protagonist and his friends will continue their work and Momonga looks forward to their work in the future. The trio pledge to strive to continue to do their best for Momonga.
After that, the group proceed while defeating the appearing enemies, and reached the 9th Floor where they see a shrine of some sort. The shrine reminds the protagonist of something he has seen in his literature, though Momonga it is vaguely familiar. Solution scouts ahead and return reporting that at the front of the building Cocytus and Narberal Gamma are present. Other than that there does not appear to be anything dangerous.
The next quest may occur and Momonga advises everyone to approach with caution. At the front of the shrine they are greeted by Cocytus and Narberal. But first Momonga asks what the shrine is for, which Narberal states to be a shrine that worships Warrior Takemikazuchi and called the Takemikazuchi Shrine. He then asks for the whereabouts of the two remaining Pleiades, Yuri Alpha and Lupusregina Beta. Narberal informs him that the two women are at the back of the shrine protecting the path to the 10th Floor. Satisfied Momonga asks if they could pass through. The two guards at the shrine state that would allow them to pass however first the group much show them their strength. Momonga asks if they wish for a duel which Cocytus responds in the affirmative. Momonga presses the issue of what would happen if he would refuse to which Cocytus states he would not be allowed to pass them. The Overlord states if they are refusing him to pass the two would be going against his command and asks if they are alright with doing that. Cocytus apologizes stating that he is obeying his intentions in protecting this shrine dedicated to his creator. Momonga sees that Cocytus's mind has been overtaken by the "New Year's mood" yet it seems that the influence s subtly affecting his judgment to protect the shrine of his creator. It would seem that he has no choice but to fight to complete this quest. Before engaging in battle, he asks Cocytus to go over the rules of battle to which the victor would be decided on one group in defeated. Moomonga can see that the influence is clouding Cocytus's mind and unable to tell him that a fight could possibly be lethal, but cautions to go easy on Cocytus and Narberal to prevent needless deaths by conctsnatly checking their HP levels.
The two groups then proceed to fight with Momonga casting his magic at Narberal and Cocytus. Cocytus lands an attack that destroys several of Momonga's skeletons and Narberal adds an attack of [Twin Mazimize Magic Electrosphere]. Momonga can see that they are not holding back and gives him all the more reason not to limit himself. The end battle sees Momonga victorious with the two in defeat before his feet. Cocytus and Narberal acknowledge their defeat and allow the group to enter the shrine as they have been sated by the battle which they found to be inspiring.
Solution Epsilon does reconnaissance inside the shrine and returns, confirming the existence of the transfer torii at the back. And also that, Yuri and Lupusregina are guarding the transfer gate. Momonga surmises that this quest will be the las one and leads the team to the maids. Yuri and Lupusregina greet the party with a "Happy New Year". Momonga asks what the two maids are doing in the area. Lupusregina answers that she is practicing kakizome, writing her aspirations for new year. It's determined by Slimeko Lupusregina is under the "New Year's mood" as she does not do her signature "~ ssu" when she speaks. Momonga then turns to Yuri, asking her why is she doing this, since the mental influence should not affect undead to an extent. Yuri admits that she left her post because it was a holiday, so she came to visit the shrine at the invitation of Lupusregina and others. However states that if his wish was for her and the others to return to their posts then she would comply. Momonga seeing that Yuri still retains her mind states that it's okay and allows her to enjoy the "holiday". Observing tha they are doing kakizome, Momonga asks if they could partake. Yuri apologizes stating that they ran out of writing materials, but Lupusregina happily states that won't be a problem as they could make more tools using the Kadomatsu Type Beast and Mochi Type Beast to make brushes and paper. Almost as if expecting a Kadomatsu and Mochi Beast appear nearby. And while Momonga doubts that the two monsters can be converted into writing mayerials, he dedices to comply with thie strange quest.
Together with Solution, Momonga kills both monsters and their remains are given to Yuri and Lupusregina who process them to make brushes and ink to write. their aspiration for the new year. Momonga is at a loss on what to write for next year, but Slimeko already has written her's to be "Eating Faster" as she wants to increase her digestion speed during her predation to help her friends. For Solution Epsilon, he has written "Acting" as she believes that it's an important skill to have after all she is operating in the outside world. Slimeko admires that idea and wishes she could use it, but her faciial expressions are limited but Solution offers to help her. The protagonist writes down either "Loyalty" or "Interaction" as he wishes to become more of an asset to his master and Nazarick.
Momonga admires the protagonists' dedication and unveils his calligraphy, "Turning Point". To explain so far, Momonga has been enthusiastic about strengthening his defenses. However, the rebirth of Nazarick has also progressed, and even if it is in the defense, the situation does not necessarily improve. Eventually, an opportunity to change policy will come and as the leader of Nazarick, he must correctly identify the opportunity. Yuri praises the word, as a wonderful aspiration. The torri gate soon glows, indicating that the path to the 10th Floor has opened signify that the group and accomplished completing the quest. Momonga and the protagonist reaffirmed their determination and set foot on the gate.
The group finally arrived at the 10th Floor of Fake Nazarick. Solution at first goes to do some recon, but is stopped by Momonga as he predicts that at the Throne Room, there will be a "Last Boss" of this "Event". Momonga further iterates that Solution went off alone, and is detected by the "Last Boss", there is a risk that she will enter the battle in a s|destructive manner. They will wait outside the Throne Room, while he sends a part of the undead unit to check on the behavior pattern of the enemy. To observe what happens he will summon Eyeball Corpses to see using [Undead Slave Sight] and check the situation.
The undead troops then march into the Throne Room where Momonga sees that a Mochi monster is sitting on the throne replica alongside two Kadmatsu monsters. Thinking it to be too simple, Momonga orders the undead to attack. The enemies in the Throne Room clash against the undead and both sides take casualties but the skeletons are victorious. Suddenly a strange white muscled being appears and destroys the remaining skeletons. The power displayed by the entity is approximated by Momonga but believes that it not to be too bad and manageable. Momonga then recalls the Eyeball Corpses back, causing Solution to wonder why they were not destroyed by the "Last Boss". Momonga tells his allies that the undead were wiped out by a powerful Chaos Beast with an acceptable attack range and power. He reports that there no apparent special effects on the surrounding area, as the fact that the Eyeball Corpses were able to return safely proves that. In addition it also proves that the enemy cannot chase anyone outside the Throne Room which they can use to their advantage if they need to retreat.
The protagonist asks what their plan will be, to which Momonga states that he and Slimeko will wait outside while he, Solution and the remaining undead forces lead the attack. From what he can tell the enemy does not fight unless in a certain range. Before that, they should use various strengthening magic, and when ready, hit the enemy with troops and enter the battle. Before going off into battle the protagoist asks Momonga to be careful.
Soon as the attackers enter the Throne Room, the entity introduces himself as Shiramochi-ō. While the entity introduces himself, Momonga starts attacking Shiramochi-ō using [Reality Slash]es but the being remains unfazed and unaffected. The entity continues on with its dialogue. Momonga notices the entity's lack of personal anger and personality indicating it is just going on a routine. He surmises that the White Advent King lacks an actual will and acts similar to a raid boss and hat the reason why his attacks are not efffective is due to that fact that the event has not yet begun. Usually in raid asualts, players needed to finish saying the prescribed wording by the opponent before attacking. If this is a game, it may have been a specification that the battle does not start until the conversation is over. That being said, the group begins to battle the entity after Shiramochi-ō, is done with his introduction.
Shiramochi-ō fights against Momonga and his forces. Momonga using [Life Essence], can see that Shiramochi-ō's HP is not too different from a single appearance type raid boss. When Shiramochi-ō prepares an attack, Momonga anticipates a peripheral ranged attack and warn Solution and his skeleton to dodge saving them. Momonga and Solution Epsilon wanting to have a short devsiove battle attack Shiramochi-ō without holding back.
In the end, Shiramochi-ō is defeated he collapses to the ground. Upon his collapse there is a flash of light and Throne Room of Fake Nazarick is returned to normal. In addition it seems that all the Crack phenomena have also vanished, indicating that by defeating Shiramochi-ō, Fake Nazarick was restored to as it was. Momonga wonders about the other effects of the "New Year's mood" and sends a [Message] to Albedo who answers asking where he is. Momonga though asks her if she is still eating tangerines with a kotatsu? The Overseer Guardian is confused as to what he is talking about, but it is enough to convince him that everything back in Nazraick is normal. He tells Albedo that he will be coming back to the dungeon soon from Fake Nazarick with the Pleiades and and Cocytus, but asks her to collect the Guardians as he will need to explain to them what happened.
Solution is please that everything worked out fine and Nazarick is safe once again thanks to Momonga. Still Momonga wonders on the New Year phenomena, asking if it was a permanent holdya thing. In a sense, he feels he should be happy and yet its a bitter feeling. However the hoiday is over and the group must return back to Nazarick.
Upon returning to Nazarick, Momonga received reports from Albedo and Demiurge at the Round Table. All Demiurge can recall was him encountering a strange Chaos Beast that appeared from the Throne of Kings and defeating. After that he cannot recollect any of the event Momonga mentioned to him, only that he distinctly recalls the faint comfort and being strangely relaxed. The same goes for Albedo stating that the mental influence made her feel very comfortable. The two apologize for not being helpful during such a sorry state, but Momonga replies it to be not their fault as the incident was completely unexpected. But it seems that everything that happen leads back to the Crack. Demiurge agrees with that assessment but even so there are many mysterious points about this phenomenon and question if it was even right to call it an attack. From what the demon gathered from the protagonist the "New Year" is a festival to celebrate the new year so why cause this phenomenon?
Momonga thinks that rather than a deliberate attack it may have been some sort of catastrophic phenomenon. For example it could have been something different from this world that may have been summoned through the throne. Even Momonga feels uncertain of his theory as the incident was too game-like, almost like a New Year's event for some games, but he can't recall if there was anything similar like this in YGGDRASIL's New Year's event.
Still it highlights that the summoning using the throne itself is an unknown phenomenon and that not all things that are beneficial to us will happen. Demiurge promises to continue his research with the Crack to find out the true cause. Though they have yet to solve this mystery, Momonga is glad it wasn't bad for everyone as they were able to celebrate the New Year and even suggests that next time they voluntarily celebrate the New Year. Albedo is more than eager to prepare for a New Year's celebration is Momonga's wishes it, but Momonga states that they would have to wait until the New Year comes again. Plus they really must get started with the scheduled meeting.
Momonga then tells asks the viewers what are they going to do with Nazarick in the future? He already decided on his aspirations. In that he needs to adapt his mind and focus it. And he thanks everyone for their continued support in restoring Nazarick and eventually aiming for a further leap forward.