Date A Nazarick

Date A Nazarick (デート・ア・ナザリック) is a collaboration game event in Mass for the Dead with characters from Overlord and Date A Live. It was released on March 19, 2020 to April 13, 2020.

Background
Spirit. A special disaster-designated life form that appeared through the Throne of Kings. There are two options. First, destroy the spirits with force. However, because of their high fighting and unknown power, there is a great risk. And the otheris to date the spirits to delay.

Incident
One day after school, Shido Istuka heads to a multi-tenant building in Tengu City, leading to a secret entrance to an underground facility of Ratatoskr. He is later joined by his classmates, Kotori Itsuka, Tohka Yatogami and Origami Tobiichi. They are talking about the upcoming physical examinations, chatting about how they can avoid it, while being secretly watched by Kurumi Tokisaki. A spacequake soon occurs, signalling the group that trouble will occur. Just as they are about to make preparations for battle, a crack in reality appears behind Kotori, sucking her into the void, followed by the rest of her friends. Kurumi watching from afar it also dragged into its grip leaving behind an empty street.

In the Great Tomb of Nazarick, Momonga and Demiurge are regularly conducting summoning experiments with the Rift in the Throne Room. As always a troop of undead guard the periphery of the phenomena. The Rift flares for a bit, spitting out Shido and his companions. While the students get their bearings, Shido fails to notice the Death Knight looming behind him as he gets up. Origami believing Shido is in danger immediately goes into her Spirit Form and attacks the undead. Kitori tries to restrain her friend in order to get a lay of the situation. However the Skeleton Warriors surrounding the Rift march in a aggressive manner, giving Origami the justification to attack. She is soon followed by Tohka who also transforms into her Spirit Form believing this to be the work of DEM despite Kotori's protest stating using corpses was a line Westcott would never cross.

Demiurge, watching the scene alongside his master is amused at this as it is the first time their summons have instantly become hostile. Momonga wants things to quiet down, so Demiurge used his skill of Command Mantra to order the newly summoned students to kneel. Shido and the others fall under its influence. Tohka is the only one who struggles to remain standing so Demiurge commands her again to kneel forcing the girl to comply. Momonga slightly intrigued that the girl was able to resist the Floor Guardian's skill, turns his attention to Shido. The young man is paralyzed on the floor and in a position where he is suffocating. Momonga orders Demiurge to help him. Just as Demiurge approaches Shido, Tohka thinking he is going to harm her friend tries to stop him but is unable to move. Looking back at her helpless, she revives the scene where Shido was injured by Westcott. Drawing from the trauma Tohka ignites her Sephira Crystal and goes into her Inverse Form. Her new form allows her to break free of the Command Mantra. Momonga seeing that the situation is growing increasingly more adversarial tells Demiurge to release the girl's friends from his power. Momonga tries to explain that there had been a misunderstanding and introduces himself as Momonga the ruler of the Great Tomb of Nazarick.

Tohka however is acting strangely unable to recognize her surroundings. Now in her Inverse Form, she spots Shido and swears revenge on him. She attacks him with [Nahemah], but Momonga saves Shido with [Wall of Skeleton]. Tenka curses at the undead interference, making the Overlord confused as this girl was this boy's ally and now has murderous intention to kill the latter. Shido attempts to thank his savior for the timely save, but Momonga suggests they concentrate on the current problem. Demiurge also engages Tenka, using [Aspect of the Devil - Eight-limb of Speed] and [Aspect of the Devil - Razor Sharp Claw] to strike her though she is unfazed. Momonga seeing her immune to Demiurge's strongest attacks, thinks that capture may not be possible. Shido tries to reason with Tohka that Momonga's group are not the enemy. She ignores him, seeing that everyone in the room is an enemy. Shido sees that Tohka is now a different person with her own "intention" and "reason". Albedo and Shalltear Bloodfallen, both fully armored arrive to assist them. Tohka seeing this as bugs raises her blade and uses Final Sword: Paverschlev. Shido warns everyone that the slash of the blade could erase everything it touches. However just as Tohka is about to swing her weapon, she stops muttering to herself before vanishing.

Momonga thinking that she is using invisibility is unable to sense her through [Sense Enemy], and neither do the Floor Guardians believe that she is invisible and that she is actually gone. The idea is seen as impossible since [Teleportation] in the New World is near impossible due to the Rifts. Kotori explains that Tohka probably used the Neighboring World to escape due to being in Spirit Form. Momonga still confused on some concepts asks Kotori to explain in greater detail.

From Kotori, Momonga learns about Spirits being human-shaped disasters that originate from the Neighboring World and that she, Origami and Tohka are able to transform into them. In Tohka's case the girl has unleashed the original source of her Spirit's true form. Usually it is sealed away however they can be awaken when a Spirit goes into Inverse as a result of them feeling intense negative emotions such as despair, usually as someone close to them is about to die or immediately after they have died. She reasons Tohka was pushed to this state when she thought Shido was in danger. Albedo and Shalltear protest at the accusation that their comrade Demiurge was going to harm anyone. Momonga is more understanding since it could have been misunderstood the intention based on Demiurge's devil-like appearance. Momonga suggests that they should concentrate on locating Tohka when she emerges from the Neighboring World. He worries that the phenomena of the spacequake may damage Nazarick, Kotori agrees but believes that if she can regain her spiritual power, and trigger a spacequake at the same time with the same magnitude, she’ll be able to cancel it. In addition, Kotori decides to refer this new Tohka as Dark Tohka in order to distinguish the two personalities. However, she states that she is unable to fight her friend as her powers makes her prone to losing control to destructive impulses over the urge of defeating another Spirit.

Aftermath
To Be Added...