Bless Nazarick! (ナザリックに祝福を！) is a collaboration game event in Mass for the Dead with characters from Overlord and Kono Subarashii Sekai ni Shukufuku wo!. It was released on July 19, 2019 to August 2, 2019.
At the Throne Room, the stones dropped from the Chaotic Beast are used in a summoning phenomenon experiment. An unprecedented presence is summoned before Momonga. The people are: a group of four adventurers from another world.
Satou Kazuma's adventurer team after completing a quest that took them to a cave are heading back to Axel. On the way to town, Kazuma relents in allowing Megumin to cast her an explosion magic in an empty plains area to satisfy her explosion fetish and her curiosity if she can break space. The young magic caster goes on an ostentatious chant of her magic spell for dramatic effect. Most of the other members such as Aqua are tired and want to get on with the spell so they can get some food. When the spell is at last released, Megumin collapses in exhaustion. She tells her friends to check if she broke space, but the others are having a rock-paper-scissors contest to decide on who does it. At the area of the explosion, a Crack appears, Aqua taking notice of the phenomena tries to warn her friends that something bad is coming. Soon the Crack begins sucking them up, Kazuma tries to flee whilst his comrades face their own distresses and emotional outbursts; Megumin pleased with the results as she has broken space, Aqua wailing helplessly like a child, and Darkness eagerly waiting for whatever perverse dangers on the other side. The entire group is sucked into the strange phenomena.
On the 10th Floor of the Great Tomb of Nazarick, Demiurge is about to conduct a summoning experiment using the Crack in the Throne Room. Momonga also present for the demonstration is informed by the Floor Guardian that the utmost care for the experiment have been implemented. Skeletons have been solidified around the Crack with Death Knights around the periphery in case of any abnormalities. So far from Demiurge's study he has determined that the overlap of the Crack and the Throne of Kings have created a special unique summoning phenomena compared to the other Cracks found outside Nazarick. Using the Crack and sacrificing a number of Chaos Stones the phenomena will call forth summons. The summons themselves so far have proven to be obedient. However what kind of summon that will appear is random, similar to a gacha machine. The experiment is initiated and soon the Crack starts to flare and blink, spitting out Satou Kazuma, Aqua, Megumin, and Darkness on the floor. Looking around Kazuma wonders if they are in Heaven, but Aqua denies this stating its full of undead.
Momonga and Demiurge watching the new 'summons' noted that they are livelier than expected. Momonga asks if they are safe with the demon assuring his master some summons from the Crack have been noted to have egos and are no threat to them. Kazuma tries to calmly assess the situation, but peace is interrupted by Aqua who impulsively lashes out and casts [Turn Undead], eliminating a troop of Skeleton Warriors. Demiurge shocked by this hostile attack prepares to purge the hostile, halts his attack when Kazuma immediately starts begging forgiveness for his friends attack. Aqua refuses to back down on her outburst reasoning her attack was justified since they are undead. To keep her quiet Kazuma drains away her mana to put on her on the ground, followed by Darkness wishing to experience the same masochist treatment. Momonga utterly confused in the spectacle wonders out loud if the summons are submitting to them, though Demiurge reiterates that the boy seems to be in charge of the group. Kazuma now speaks on behalf of his adventurer party, explaining that Aqua's attack was the result of her mental defect towards the undead. Momonga states that what she did was still a hostile act and cannot be easily forgiven. But Kazuma manages to plead on Aqua behalf taking responsibility for her actions, despite Aqua's inconsiderate prejudice of the undead. Kazuma asks where they are to their two mysterious hosts. Demiurge having not forgiven them for their affront believes that the group should be disposed of. Momonga thinks otherwise as they are valuable specimens and should see if they can glean for more information. Demiurge is convinced to withhold his wrath over the 'summons' until they gain more information. Momonga then asks they introduce themselves. Satou Kazuma then provides his name, which Momonga takes an interest in being Japanese before they delve further into details.
Momonga hearing from Kazuma's testimony of being from the city of Axel and beings such as the Demon King are unfamiliar to him. Demiurge suggests that the Crack may not like how undead are created, in that they are summoned from the spot. He surmises perhaps that the Crack unique situation in Nazarick connect to other locations that sucks up beings on the other side. This is so unlike how the Chaos Beasts emerge from and judge this to be an irregular case. They are interested to learn that the Crack on the other side was actually caused by Megumin's explosion magic. Momonga is most interest in that ability comparing it to a World Class skill. Though Momonga knows his side holds most of the cards, he decides to forgo hostile action. Before he declares his sentence over Kazuma and his companions, Kazuma states that he understands that returning home may be difficult and asks Momonga to hire them in the mean time as a way to make up for killing Momonga's summons. Aqua reluctantly agrees to the settlement, along with Darkness and Megumin, who believes that she will have more chances to cast Explosion magic.
The next day, Kazuma and his team are busy cleaning the hallways of Nazarick on the 9th Floor. Kazuma finds this to be a good change of pace. He asks for Megumin to pass a rag while cleaning the floor. She tells him not look up her skirt, drawing Darkness into the conversation with her perverted fantasies. Kazuma notices Aqua fuming at cleaning the domain of an undead, seeing it below her as a goddess. The adventurer distract her from her tirade by asking her to purify the water in his cleaning bucket. Seeing a way to be useful she complies, and basks in her friends praise of her power, until she realizes what she is doing. She objects to being a servant to undead, stating the beings in Nazarick are obviously evil. Kazuma states that it can not helped as they might have been killed, plus they are in this situation because she attacked first. Aqua insists that it was a justified self-defense as undead are always the enemy, and not only that there was a demon in the room.
Megumin and Darkness point out that not all undead are evil aligned, bringing Wiz up as an example. Kazuma noted that the demon with glasses was a dangerous opponent to begin with. Better to bite down and hold it in than risk certain death and try to escape he also adds. The life so far as acting as menials for Nazarick is good, as they get a decent meal better than they eat at a bar. Megumin complains that she wants to cast Explosion magic at least once a day. Kazuma believes that she will get her chance once an escort is available to take them outside the tomb.
Suddenly they are approached by a young pink haired girl named Slimeko. Kazuma thinks that she is cute until he learns that she is actually a slime. Slimeko asks them to come outside with her, which causes Kazuma to think that she is taking them to be executed. Slimeko states that is not the case, but Momonga is interested in a demonstration of Megumin's Explosion magic.
Momonga wanting to do an analysis of Megumin's ability, the potential of Explosion magic being able to "crack space", has three of his servants: Slimeko, Narberal Gamma and the protagonist placed in charge of the demonstration. The trio take this experiment to the vicinity of the Great Forest of Tob, where Slimeko introduces her colleagues to the four adventurers from another world. Kazuma seeing Narberal muses that she is beautiful, causing the battle maid to art cold towards him calling him an inferior life form. The maid's harsh words however serve as a lure to Darkness who soaks up the verbal abuse of the other woman much to the confusion from the members of Nazarick. When Kazuma explains that Darkness is a masochist the group moves to the conduct the experiment. Megumin is eager to display her abilities and prepares her chanting. Meanwhile a swarm of Giant Beetles attack, forcing the group to handle them as Megumin is still casting her spell. When she finally releases her magic and collapses from the mana exhaustion, Momonga watching the scene via the Mirror of Remote Viewing, is impressed that the spell eliminated a large number of enemies in a single shot, though he still doesn't see it unconditionally creating a Crack. Later he wonders why the magic caster collapsed.
To get more information, he calls Narberal to transfer his [Message] to Kazuma so he can exactly know the details of the magic. From Kazuma they converse and he is surprised to learn that Explosion magic is the only spell she knows, which Momonga findings a hassle. The two begin discussing the specifics on Megumin's power in greater detail.
Later in an isolated area outside Nazarick, Kazuma tells his team about his conversation with Momonga, claiming the fearsome undead was quite friendly contrary to what they thought. Aqua is skeptical that an undead could be friendly, Megumin and Darkness suggest that Kazuma is brainwashed. Kazuma states that is not the case as when he spoke to Momonga, he actually just a normal person who listens. Mare Bello Fiore overhearing Kazuma’s conversation is happy at Kazuma’s opinion of his master. Kazuma tried to flirt with Mare only to be corrected that he is a male. After earning criticism from his peer who called him a lolicon, Mare informs the group that Momonga has another task for them to perform outside of Nazarick. They are joined by Aura Bella Fiora who takes over from Mare. Megumin wonders if she will be allowed to cast Explosion magic. Aura states that is not the case, but there will be opportunities for her ability. Megumin cannot wait, and is impatient to wait. As a precaution, Kazuma uses his mana drain ability to take ensure she does not premature use her spell and cools down. Kazuma asks the two representatives from Nazarick there next task. The dark elf states it is merely pest control as their transportation route, have been plagued by a specific monster. Before they take the task, Aqua asks if the monsters they will be facing are frogs. Aura replies the monsters are not frogs, drawing a collective sigh of relief from the adventurers. Seeing the elf's confusion, Kazuma states that in the past they experienced a trauma fighting frog-type monsters.
The monsters turn out to be a special breed of slime called Fiber-Eating Slimes, that while consume plants can also devour clothing. Aqua is covered by one such monsters much to her horror, and cries for help. Aura states that these monsters are not that dangerous as their acid is not so potent to harm flesh, and watches the adventurers run around in chaos. So far only Aqua is being target making, Aura wonder if the girl has some high quality clothing. Megumin decides to help and has Kazuma return her mana to cast her Explosion magic. The managed to get Aqua out of her clothes and throw it into the sky and the slimes are drawn to it allowing the magic caster to eliminate them all. After the incident Aura collected the pieces of Aqua clothing somewhat restoring Aqua's dignity.
A few days after the adventurers were summoned, Momonga is speaking with Albedo on her views of the visitors from another world. Albedo reports that the group while useful in their tasks have yet to convert to being members of Nazarick. She finds Aqua to be concerning, given her undisguised hostility towards the undead and recommends disposing her. Momonga believes such actions are not necessary as they are still under his protection. On the topic of the Explosion magic, despite being demonstrated every day, they still have not witnessed it to create a Crack. Either Megumin is hiding her ability or there were special conditions that allowed her to achieve the phenomena. Albedo believes there might be clues in studying the girl's equipment. Momonga seeing it as a valid theory, decides to call Pandora's Actor.
Momonga brings Megumin and Pandora's Actor to the Round Table Room, however the merely stare at each other in mute silence for a time. After studying each other, both introduce themselves in an exaggerated and posed manner. Megumin is highly impressed with Pandora's Actor's clothing and mannerism, thrilling the NPC who compliments on the magic caster's sense of taste. Momonga has to step in to get them back on track. Pandora's Actor after appraising Megumin's equipment confirms that there is nothing abnormal. Momonga disappointed watches the two kindred spirits bond.
Outside Nazarick, Darkness is alone with Solution Epsilon, who watched the masochist take pleasure in the clothing eating slimes devouring her clothes to satisfy her dark perversions, effectively making herself as bait. Solution seeking to find a way to get Darkness's cooperation gives her a 'toy' she acquired from Neuronist Painkill's torture chamber. Darkness upon acquiring finds it to be gratifying and sees Solution as a worthy patron.
Much later in the Lemegeton, Kazuma and his friends are preparing to subdue new monsters called Chaos Beasts. The group is pleased that Momonga is acknowledging their work fro Nazarick. Aqua is unmoved by the praise from Nazarick, and sees that Kazuma, Megumin, and Darkness are brainwashed. Lupusregina Beta now on duty for surveillance duty with the adventurers in the Throne Room. Since there are undead around the area, Lupusregina states that Aqua will be excused from this mission due to her undead phobia. Aqua is surprised by this though Kazuma tells her that she should take it as a blessing.
In the Round Table Room, Momonga asks Demiurge on the progress of the adventurers. The Floor Guardian reports that they have so far under Lupusregina's they have performed without any issues. He is concerned on the issue of the blue-haired girl. He asks why Momonga has been giving sch an impudent girl such mercy to allow her to ignore his orders. From Satou Kazuma, Momonga learned of many unbelievable things of his world. One tidbit of information he learned was that Aqua is a "goddess". Demiurge wonders what kind of profession is a goddess. Momonga is unsure on her status, and he does not wish to get involved into a theological debate over the existences of gods. However he has been observing her and she has displayed strange abilities like purifying water, high-level healing magic etc. It brings the possibilities of resurrection magic without penalties and losing levels. Demiurge sees the advantages in keeping her alive, though compared to the other three adventurers she appears to be head strong and uncooperative. Despite this Momonga wants to gain her cooperation and use coercion as a last resort. Demiurge advises his master to allow him to handle the situation as he may have a method to gain her confidence.
Left on her own, Aqua finds her way to the 6th Floor, where is is shocked by the artificial sun and forest environment. There she meets the butler, Sebas Tian and Cocytus. Aqua is initially off put by the appearance of the latter due to his monstrous appearance. Sebas with calmness asks if its true that Aqua is a goddess. Aqua states so what is she is? Sebas Tian replies that his master Momonga is interested in gaining her respect. He has been sent to show her hospitality and the utmost respect Momonga has of her. Aqua surprised is not sure about offering her blessings to an undead. So Sebas Tian offers to entertain her by allowing her to observe and participate in his daily work he does for his master. Aqua interested decides to accept the offer, even though she believes that her opinion of the undead will not change from this one experience.
Around fifteen minutes later, the goddess is enjoying herself, being served tea and snacks by the butler and insect. They are interrupted when Sebas informs Aqua that he and Cocytus will need to prepare for the Chaos Beasts that the Crack will produce. As they excuse themselves, Aqua invites herself into their mission as a method to repay their hospitality. The three then head to the Crack and successfully slaughter the invading monsters. To celebrate their victory Sebas suggests heading to the bar run by Sous-chef for a round of drinks which Aqua eagerly agrees to.
At the Amphitheater, Momonga personally congratulates the adventurers for the tasks they have complete for Nazarick. As a reward he welcomes them to join the ranks of his subjects. Kazuma, Darkness and Megumin, after their personal experience in interacting with a few of the tomb's inhabitants find the offer to be a good deal. They turn to Aqua who has been silent in much of the discussion. When she at last speaks, she admits that living this new world, serving as servants to Momonga would be a logical choice. However she rejects his offer holding onto her pride as a goddess stating she would not serve a filthy undead. Kazuma angst at her disrespect to toward the host fears that she may have invoked Momonga's wrath and death sentence. To his shock, Momonga laughs in mirth, admiring Aqua's spirit. Seeing that cooperation and simple coercion is ineffective, he offers them a deal. If they can defeat him in a 4 vs 1 match then he will allow them to leave the dungeon peacefully. If they lose then they must submit to Nazarick. Aqua initially is hesitant to accept the terms, until Momonga goads her into fighting, calling her being afraid of the undead, out of prode she accepts the challenge must to Kazuma's chagrin. Now crossing the point of no return the adventurers prepare to battle against Momonga.
Aqua attempts to land God Blow on Momonga. but he easily counters her attack with [Wall of Skeleton]. She injures her hand, slightly, and complains that it was a cheap trick of him. Momonga regards this as a childish tirade with Kazuma in agreement and the battle continues. Even with all four of them fighting, they are outmatched by the Overlord, Megumin's Explosion magic not even having any effect on the ruler of Nazarick. Aqua refuses to admit defeat, even when she faces, Momonga's stifling Undead Aura which Aqua respond in igniting her own Holy Aura. Just as the two were about to clash their powers, Aqua receives a call from Eris, asking where has she been. Aqua speaking to her out loud tells her of the situation and the other goddess agrees to arrange for a pick-up of the group. Kazuma learning they are about to soon return home, tells Darkness to pick up an exhausted Megumin. Turning back to Momonga who has been watching the scene with utter confusion, Kazuma hastily offers an apology before he and his group make a run for it. Demiurge asks if he should prevent them from leaving. Momonga tells him there is no need, believing that they have made their choice.
Kazuma awakens to find himself back in the grassland plains where Megumin had caused a Crack. The sun is setting and he wonders if there are in their world. Aqua tries to take credit of their fortune in returning home. Kazuma looking behind finds the proof that he needs to confirm that he is back in their world. Discreetly moving away from Aqua, the goddess wonders where he is going. A loud croaking sound is soon heard and too Aqua's horror a Giant Toad is looming behind her. Kazuma, away from his friend's antics, silently gives a prayer to the Supreme One asking him for his mercy upon him.