Kumeno first appears in the second episode, "Transistor Smartphone". As a high school student, her friendly and outgoing nature starkly contrasts with classmate Koizumi’s solitary, withdrawn demeanor. Kumeno persistently attempts to connect, waving and greeting Koizumi despite her disinterest in social interaction and constant smartphone use.

During a quiet moment, Kumeno approaches Koizumi directly, triggering a confrontation where Koizumi questions her motives. Their exchange escalates unexpectedly into a sharp dispute, irreparably damaging any potential friendship. The incident leaves Kumeno with lasting regret and unresolved emotions. Years after graduation, she reflects on this failed friendship attempt while standing on a balcony, still pondering the encounter and its bitter aftermath. The narrative implies mutual apologies never occurred, leaving future reconciliation uncertain.

Kumeno’s story explores themes of miscommunication and unresolved adolescent relationships' enduring impact. Her character design features pigtails, consistent with typical high school depictions.