The four princes of Grannzreich—Kai, Bruno, Leonhard, and Licht— continue to compete for the right to their kingdom's throne under the guidance of their beloved royal tutor, the competent yet childlike Heine Wittgenstein. One day, during a political visit to Grannzreich, the king of the neighboring Romano Kingdom arrives at the royal palace with his twin sons, Ivan and Eugene. In the hopes of befriending the twins, Heine and the four princes meet their visitors, but their efforts are thwarted instantly when the two twin princes declare that they refuse to address those who will never reach the throne. Dispersing the tension between the boys, Heine reveals that he, upon their father King Victor von Grannzreich's request, will be tutoring the Romano princes alongside the Grannzreichs for the duration of their stay, in hopes of strengthening the future relations between the two kingdoms.

Recap voice dramas of main characters posted online and later included in Blu-ray volume 2 of main series.

Hisoka was an orphan who was raised by Yukitaka, the present head of the worldwide Jinsei Corporation, with the help of his right-hand man Daisuke. He was adopted for the sole purpose of working both publicly and secretly for his daughter Orihime, who was next in line to inherit the business. That’s why he did not hesitate when he was asked by Yukitaka to attend the same school as her and serve as her bodyguard in secret. The only problem was that her school was the refined Saint Ceral Girls’ Academy, which was closed to boys. He didn’t know it at the time, but it would be a major turning point in his life. (Source: VNDB, edited)

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.