Samejima, a demon linked to Januar Ein, embodies masculinity and fierce loyalty. Born with innate demonic traits and a natural "Manly Aura," his vivid red hair stands out in a delinquent style, paired with black eyes. He initially wears a black school uniform: a gold-buttoned long-sleeved short coat left open to expose his chest, black pants fastened by a red-and-white belt, and white socks. Later, he adopts a black button-down shirt—often unbuttoned or layered over white—with black pants and shoes. His Manly Aura creates an illusion of increased height.

Driven by ideals of being a "real man," he prioritizes protecting friends above all, especially in danger. He intervenes abruptly using illogical magic to aid others. After overcoming temporary self-doubt when questioned about his nonsensical statements, he becomes impervious to such critiques.

His Manly Aura grants defensive strength, rapid mid-battle healing, persuasive influence, and the ability to reach imperiled friends across barriers. He sustains injuries solely while protecting others. He also employs pain-taking magic to absorb allies' wounds. Equipment includes a uniform jacket that occasionally deflects attacks and stores 163 protective watches from friends. Later, he wields a "Soul" belt connected to Janua, enabling fusion to merge their powers.

His involvement begins when a dagger he gifted indirectly saves Janua from Zwei. He later shatters Janua's brainwashing by punching him in a dimensional rift, then shields escaping allies by absorbing their injuries. After protecting Alba from Juli's assault, he collapses from self-doubt but recovers. Subsequently, he rescues Ruki from September during a soccer match and declines to interfere in Janua's marital struggle with Hasegawara, advising respectful rejection. Finally, he battles Rchimedes alongside Mortemone II, regenerating a severed arm using his master's pocket watch until Rchimedes exploits his protective instinct toward Mortemone. Janua teleporting reinforcements concludes the conflict.