Overlord

Overlord is a dark fantasy isekai anime (4 seasons + a movie) based on Kugane Maruyama's light novels.

Quick synopsis:

In the final moments before the popular VR MMORPG YGGDRASIL shuts down forever, dedicated player Momonga (real name: Satoru Suzuki) stays logged in until the servers close. Instead of kicking him out, he finds himself trapped inside the game world as his max-level undead overlord character, Ainz Ooal Gown — a powerful skeletal mage.

The NPCs of his guild's massive tomb base, Nazarick, have gained true sentience and fanatical loyalty to him. Suddenly thrust into the role of an all-powerful ruler in a new, real-feeling medieval fantasy world filled with kingdoms, monsters, and adventurers, Ainz sets out to:

• Explore and understand this new reality
• Secure his position and the safety of Nazarick
• Expand his influence (often ruthlessly)

What follows is a mix of overwhelming power fantasy, strategic conquest, political maneuvering, and occasional dark humor. Unlike many isekai protagonists who start weak and grow, Ainz begins god-tier strong — so the story focuses more on how an emotionally detached, calculating "corporate salaryman brain" in an evil overlord body rules, experiments, and deals with misunderstandings from beings who see him as a supreme being.

It's famous for its subversion of typical isekai tropes, epic battles, loyal (and sometimes terrifying) floor guardians, and Ainz's internal panic when everyone assumes he's an infallible genius.

If you're into villain protagonists, OP main characters done right, and "what if the final boss became the MC?", it's a classic.