It is the start of Takatoshi Tsuda's second year as the put-upon vice president of the student council and his sister Kotomi is entering school as a first year. New friends and double entendres are made. (Source: ANN)

Ainz Ooal Gown, the undead sorcerer formerly known as Momonga, has accepted his place in this new world. Though it bears similarities to his beloved virtual reality game Yggdrasil, it still holds many mysteries which he intends to uncover, by utilizing his power as ruler of the Great Tomb of Nazarick. However, ever since the disastrous brainwashing of one of his subordinates, Ainz has become wary of the impending dangers of the Slane Theocracy, as well as the possible existence of other former Yggdrasil players. Meanwhile, Albedo, Demiurge and the rest of Ainz's loyal guardians set out to prepare for the next step in their campaign: Nazarick's first war… Overlord II picks up immediately after its prequel, continuing the story of Ainz Ooal Gown, his eclectic army of human-hating guardians, and the many hapless humans affected by the Overlord's arrival. [Written by MAL Rewrite]

After an embarrassing high school class reunion with their successful classmates, who have "proper" jobs, relationships, and even children, the Matsuno sextuplets return home to sulk about their status as NEETs. They spend the night drinking away their sorrows, eventually falling unconscious, until they awaken in a strange world of memories, centered around one of the brothers' biggest high school regret.

As the sextuplets navigate this memory world, they encounter their embarrassing past selves from high school, as well as those of their friends. All the while, they try to uncover whose regret was great enough to trap them in this strange world, so that they can make their way back to reality. However, they're running out of time; this world of memories is unstable, and the sextuplets may lose their chance to make things right if they're too slow....

Not all is normal in Tomobiki, even by its standards. The students have been preparing feverishly for the first day of the student fair, which is scheduled to go on the next day. However, problems arise when some begin to notice that the next day simply will not come. As the students begin to try to find the reason for the problem, their beliefs about reality and the world of dreams are challenged.