Bless Nazarick!

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.

Background
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.

Incident
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-scissor contest to decide on who does it. At the area of the explosion, a Rift appears, Aqua taking notice of the phenomena tries to warn her friends that something bad is coming. Soon the Rift 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 Rift 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 Rift 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 Rift and the Throne of Kings have created a special unique summoning phenomena compared to the other Rifts found outside Nazarick. Using the Rift 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 Rift 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 Rift 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 spectale 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 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 Rift may not like how undead are created, in that they are summoned from the spot. He surmises perhaps that the Rift 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 Rift 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 Rift. 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.

Aftermath
To Be Added...