"Overlord" is set in a virtual reality MMORPG called Yggdrasil, where players immerse themselves in a fantasy world filled with magic, monsters, and guilds. The story begins as the game’s servers are about to shut down permanently. Momonga, a powerful skeletal mage and the leader of the guild Ainz Ooal Gown, decides to stay logged in until the very end. When the shutdown time passes, Momonga discovers that the game world has not disappeared, and he is now trapped in his avatar’s body, with the NPCs of his guild’s headquarters, the Great Tomb of Nazarick, gaining sentience and personalities.

Momonga, now adopting the name Ainz Ooal Gown to represent his guild, resolves to uncover the truth behind this phenomenon while maintaining the legacy of his guild. He assumes the role of an overlord, ruling over the NPCs who revere him as their supreme leader. The NPCs, including the loyal and intelligent Albedo, the battle-crazed warrior Cocytus, and the cunning Demiurge, are fully devoted to Ainz and strive to fulfill his goals, often interpreting his actions in ways that amplify his perceived greatness.

As Ainz explores this new world, he discovers that it is not merely a continuation of Yggdrasil but a fully realized reality with its own rules, inhabitants, and conflicts. To ensure the safety and dominance of Nazarick, Ainz begins to gather information, forge alliances, and eliminate threats. His actions often involve strategic manipulation, as he balances his desire to protect his guild’s legacy with his growing curiosity about the world’s mysteries. Along the way, Ainz encounters various factions, including human kingdoms, demihuman tribes, and other powerful entities, each with their own agendas.

The narrative delves into themes of power, morality, and identity as Ainz grapples with his transformation from a human player to an undead overlord. His interactions with the NPCs, who view him as an infallible leader, highlight the complexities of leadership and the weight of responsibility. The series also explores the perspectives of other characters, both within and outside Nazarick, providing a multifaceted view of the world and its conflicts.

"Overlord" combines elements of fantasy, strategy, and dark humor, with a focus on world-building and character dynamics. The story progresses through Ainz’s efforts to expand his influence while navigating the moral ambiguities of his actions, often blurring the line between hero and villain. The series is notable for its intricate plot, diverse cast, and exploration of power dynamics in a richly detailed fantasy setting.