Kei Odagiri works in the same office as the protagonist, Koshiro Saeki. In this setting, he serves as a colleague and a secondary character whose primary function is to offer contrast to the main narrative.

Kei is defined by his open and immature fascination with young girls. He is consistently described as the office pervert, with a stated preference for having a teenage girlfriend. This personality trait is used as a source of comic relief, providing occasional lighter moments that stand in stark opposition to the serious and anguished tone of the central story. His behavior is deliberately presented as shallow and inappropriate, which highlights the complexity and deep moral conflict experienced by Koshiro, who is hiding a far more serious and emotional attachment to a younger girl.

After meeting Nanoka, Koshiro’s younger sister, Kei revises his stated fantasy; he begins to express a desire for a younger sister himself. This reaction underscores his inability to understand the gravity of the situation, and his presence in the story primarily exists to emphasize, by contrast, the genuine and tortured feelings that define the main characters’ relationship. He has no significant personal development or arc, remaining a static figure whose actions do not drive the plot forward.