Jishou Maou to Chuuni Cluster

Kamishiro Kei vanished for six months when he was young and has no memory of what happened during that time. Now a high school student, he firmly believes he is from the underworld and the rightful heir to the demon lord throne. His childhood friends, twin sisters Noibara Yuzuki and Akezuki, are used to his delusional worldview and play along with his fantasy, acting as his loyal servants.

Kei's daily life revolves around his self-proclaimed demon lord identity and the antics of his friends who humor his delusions. But as he navigates high school, his strange beliefs attract attention, and the line between fantasy and reality begins to blur. What really happened during those missing months, and how far will his delusions take him?