Ecstas Online

Ecstas Online (エクスタス・オンライン) is a light novel series by Masamune Kuji with illustrations by Tsukune Taira.

Plot
In Minami Myojin Public High School, Kakeru Doumeguri stands the lowest in the school caste. But in the VRMMORPG 《Exodia Exodus》, he stands out the highest as the game's most powerful demon lord, Hellshaft. Somehow, Kakeru is reincarnated as his enemy character until one day, a player suddenly appears in front of his eyes, his classmate and love affection, Asagiri Ririko. For reasons unknown, Asagari and the rest of the players are trapped in the game, and the only way out is to clear the game by defeating the Demon Lord. But Kakeru realizes from another fact that everyone’s lives would be in danger if that happens. To save everybody he cares about,  Doumeguri/Hellshaft attacks his classmates with his strongest ability, the “Forbidden Power” (Adult Mode)! It's up to both Human and Demon Sides to cooperate in order to return home.