Kojiro Toyama emerges in the narrative's second season. His surname combines the characters for "outside" and "mountain"; his given name incorporates "small," "next," and "son," reflecting traditional naming conventions.

He serves as a primary antagonist, driven by a fractured psyche that manifests a secondary personality compelling him toward violence, including murder. This instability fuels intense internal conflict, progressively eroding his mental state and hindering his ability to form stable alliances or motivations. His actions consistently obstruct the protagonists' progress throughout much of the season.

A pivotal shift occurs during the climax, where Kojiro moves from obstructing the protagonists to reluctantly cooperating with them. This late-stage development forms a redemption arc. His fractured identity stems from a traumatic past, though specific details of his origins remain undefined. His role concludes with him fighting alongside former adversaries in the final confrontations.