White Sliver and the Undead King

Death Ruler and Berserker is a collaboration game event in Mass for the Dead with characters from Overlord and Youji Senki. It was released on November 8, 2019 to November 22, 2019.

Background
A summoning phenomenon caused by the stones embedded in the Throne of Kings and the stones dropped from the Chaos Beasts. In front of Momonga, who witnessed the verification experiment, six new visitors from another world appear. The Imperial 203rd Aerial Mage Battalion belonging to the Imperial Army - a military unit headed by a "little girl."

Incident
Maj. von Degurechaff and the members of the Imperial 203rd Aerial Mage Battalion are currently in the air testing out the Elenium Type 97 ‘Mobile Assault’ Operation Orb for Professor Adelheid von Schugel. During Tanya's activation of the magic equipment, her orb malfunction and it at the verge of a meltdown. Seeing her soldiers around her, she orders them to distance themselves from her to save themselves. The others are conflicted to what to do when a Rift suddenly appears and sucks the Major followed by the rest of her team into its grip. The soldiers land in the middle of the ruined Throne Room on the 10th Floor of the Great Tomb of Nazarick. Recovering slightly they find themselves amongst a troop of Skeleton Warriors, led by a demon and a robed undead. Tanya upon seeing the monsters originally thinks perhaps they are costumes and at an amusements park in the Unified States, however changes her ind when she notices the realistic qualities of the so-called costumes. The members of the battalion tense and grip their weapons at the confusion of their new surroundings. The robed undead says that the summoning was successful though wonders if the group would be sent back. The undead introduces himself as Momonga, and request who in the group speaks for them. Initially mistaking Matheus Johan Weiss as the leader, followed by the denials of Wilibald Koenig, Rhiner Neumann, and Vooren Grantz, Momonga comes to Viktoriya Ivanovna Serebryakov who directs him to Tanya von Degurechaff. Momonga is surprised as Tanya is just a little girl.

The two leaders then discuss the current circumstances they find themselves in. Momonga after hearing Tanya's story of how her team came through a Rift is certain acted as a doorway to another world and quite different to the one that it previously connected to given the level of technology and culture. Likewise Tana thinks to herself and suspects this all to be Being X's meddling. Momonga decides to allow Tanya's group to stay within Nazarick for the time being, in hopes of utilizing their unique skills for Nazarick's benefit. To ensure her soldiers' safety Tanya decides to accept the hospitality offered by the Overlord while they figure out a way to return home.

Aftermath
To Be Added...