Roki Demon serves as a secondary character and mecha pilot within the Neo International Defense Force (NIDF), operating alongside Shu Aiba, Shu Nanao, Ton Kiri, Aguri Io, and Itsuki Sasara. Presumed dead after an early major confrontation, Roki and most of his squad later resurface as "transformed" humans. Exposure to the Book of the Dead during the incident rendered them semi-Necrodivers, granting abilities distinct from Shu Aiba's full Necrodiver state.

This transformation endows Roki with unique combat capabilities and named special attacks. He frequently reappears in opposition to Shu Aiba, driven by motivations like jealousy, unresolved past conflicts, or differing perspectives stemming from their transformation. Physically, Roki bears distinctive face markings. His narrative role is that of a recurring character and intermittent rival in later story arcs.