Ryōta Iijima is the school guidance counselor, outwardly friendly and supportive of students' ambitions. His appearance fits a stereotypical teacher: glasses, a brightly colored sweater vest, and a hair clip securing his bangs. This cheerful facade conceals his true role as the vessel for the dream demon Mystleteinn.

Iijima secretly orchestrates a scheme where he forces students to become vessels for other dream demons. Mystleteinn then kills these demons, stripping the human hosts of their goals and ambitions and leaving them apathetic or catatonic. His methods reveal profound sadism; after Mystleteinn defeats one student's dream demon, Iijima assaults the unconscious girl by repeatedly kicking her head, causing visible bloodsplatter and implying potentially fatal intent.

As an anime-original antagonist, Iijima has no direct manga counterpart. He amalgamates traits from several manga characters: the guidance counselor role (Osuga), the position as class instructor (Hasumi), and the thematic focus on consumption/appetite (Kyō Shiragi). His storyline is confined solely to the anime adaptation.