Comprehensive Manga: The Strongest Demon King Starting from Demon High School

Roy traveled to the world of Devil High School and became Gurefia's younger brother, the sole heir of the Lucifergus family.

And obtained the demon chess piece system, from then on Roy embarked on the path of traveling across all realms to conquer his followers and become the strongest demon king.

Busujima Saeko: I swear on the honor of the Busujima family, I am willing to become Roy's knight.

Butterfly Ninja: As long as I can save my sister, I am willing to become Roy's soldier.

Esdeath: If you want me to be your queen, then defeat me!

The main world is the devil high school world.

Across the World: Academy Apocalypse—Demon Slayer: Kimetsu no Yaiba—Pokémon—The Crimson Eyes—Kobayashi’s Dragon Maid—God Eater—To Be Continued