Asmodeus emerges as a demonic antagonist targeting Rika Manabe during summer break. He attempts to kidnap her, declaring himself a devil, but the angel Luvriel intervenes. Their initial confrontation, featuring Asmodeus's demonic powers including tentacle attacks, ends in a stalemate leaving both weakened.

Following this defeat, Asmodeus shifts tactics, exploiting human vulnerabilities. He encounters Meimi Otonashi, a classmate of Naoto and Rika consumed by jealousy after witnessing Naoto confess to Rika. Asmodeus manipulates Meimi's emotions, transforming her into the villainous Misty May to continue his attacks against Rika and Naoto.

Visually, Asmodeus presents a childlike androgynous appearance with short gray hair, red eyes, and a light gray color scheme. His distinctive attire includes a crop top, shorts, and a belt, often accompanied by wings—a stark contrast to his cunning, fallible demonic nature prone to failed schemes.

His relationship with Misty May deteriorates rapidly. Though he created her, she treats him with contempt during her transformed state. This sparks a cycle of retaliation where Asmodeus punishes Meimi in her human form, highlighting his vengeful and petty tendencies beneath a self-perceived sophistication.

Asmodeus's influence wanes after Rika becomes the angelic warrior Djibril through Luvriel's guidance. Djibril ultimately defeats him, concluding his primary role.

Later media introduces Rococo, identified as Asmodeus's sister, who seeks revenge for his defeat by corrupting Rika into a dark version of Djibril. This indirectly extends Asmodeus's narrative impact through familial ties, though he does not reappear directly.

No concrete information exists regarding his origins, motivations beyond causing chaos, or activities after his defeat. His legacy persists through Rococo's actions and the corruption of other characters like Misty May.