Barely surviving in a barrel after passing through a terrible whirlpool at sea, carefree Monkey D. Luffy ends up aboard a ship under attack by fearsome pirates. Despite being a naive-looking teenager, he is not to be underestimated. Unmatched in battle, Luffy is a pirate himself who resolutely pursues the coveted One Piece treasure and the King of the Pirates title that comes with it. The late King of the Pirates, Gol D. Roger, stirred up the world before his death by disclosing the whereabouts of his hoard of riches and daring everyone to obtain it. Ever since then, countless powerful pirates have sailed dangerous seas for the prized One Piece only to never return. Although Luffy lacks a crew and a proper ship, he is endowed with a superhuman ability and an unbreakable spirit that make him not only a formidable adversary but also an inspiration to many. As he faces numerous challenges with a big smile on his face, Luffy gathers one-of-a-kind companions to join him in his ambitious endeavor, together embracing perils and wonders on their once-in-a-lifetime adventure.

The final hour of the popular virtual reality game Yggdrasil has come. However, Momonga, a powerful wizard and master of the dark guild Ainz Ooal Gown, decides to spend his last few moments in the game as the servers begin to shut down. To his surprise, despite the clock having struck midnight, Momonga is still fully conscious as his character and, moreover, the non-player characters appear to have developed personalities of their own! Confronted with this abnormal situation, Momonga commands his loyal servants to help him investigate and take control of this new world, with the hopes of figuring out what has caused this development and if there may be others in the same predicament.

The Holy Grail War is a battle royale among seven magi who serve as Masters. Masters, through the use of the command seals they are given when they enter the war, command Heroic Spirits known as Servants to fight for them in battle. In the Fifth Holy Grail War, Rin Toosaka is among the magi entering the competition. With her Servant, Archer, she hopes to obtain the ultimate prize—the Holy Grail, a magical artifact capable of granting its wielder any wish. One of Rin's classmates, Shirou Emiya, accidentally enters the competition and ends up commanding a Servant of his own known as Saber. As they find themselves facing mutual enemies, Rin and Shirou decide to form a temporary alliance as they challenge their opponents in the Holy Grail War.

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.