Kumiko Komori is a transfer student who arrives at Kikumoto High School, instantly becoming the first romantic interest of the protagonist Samatarou Kamiyama. She is described as slender and conventionally pretty, with dark hair and dark eyes. Her outward demeanor is gentle and reserved, often appearing somewhat timid and easily influenced by the actions of others around her. Despite this shy exterior, she demonstrates a kind and caring nature, especially toward those she grows close to, and she is capable of warmth and loyalty. She is also portrayed as academically capable and athletically talented, though these traits are secondary to her emotional arc.

Unbeknownst to almost everyone, Kumiko is the daughter of a female devil. Since her demonic powers began manifesting during middle school, she has been forced to look after her mother by feeding her the energy of human souls. This burden defines her hidden motivations: she longs to escape a fate that destines her to a life of draining others and being bound to her demonic lineage. She is caught between her instinct to survive in the only way she knows and a genuine desire to be free of that life, a conflict that intensifies as she forms real connections in the human world.

Her role in the story is pivotal. Her arrival sets the central romantic conflict in motion, prompting Samatarou to pursue love without relying on his divine family’s powers. After being subjected to emotion‑influencing antics by members of Samatarou’s household, Kumiko develops genuine feelings for him when he saves her from a dangerous fall. She later transfers back to the same school and attempts to build a closer relationship with him, but this fragile bond is undermined when the truth about her demonic heritage comes to light. In the final act, she confesses everything and pleads for Samatarou’s help to break free from the devil’s path.

Kumiko’s key relationships revolve around Samatarou, who represents both her first love and her hope for salvation. Initially the object of a crush, she comes to depend on him as a lifeline. Her presence also complicates the longstanding bond between Samatarou and his guardian angel Tenko, creating a triangle of unspoken feelings. Her relationship with her mother is one of coerced care and parasitic obligation; she is essentially a tool for her mother’s survival. Interactions with the mischievous Kamiyama family—particularly Misa and Meme—initially manipulate her emotions but also inadvertently push her toward self‑awareness.

Over the course of the narrative, Kumiko undergoes significant development. She begins as a seemingly normal girl hiding a monstrous secret, moves through a phase of confused feelings and reluctant compliance with her mother’s demands, and ultimately reaches a point of desperation where she actively seeks help rather than remaining trapped. In the story’s resolution, after Samatarou defeats the demonic force within himself, Kumiko is saved and undergoes a transformation, becoming an angel. This change symbolizes her final escape from her inherited darkness and her attainment of a new, benevolent identity.

Her demonic lineage grants her the ability to channel or facilitate the absorption of human soul energy, a power that primarily served to sustain her mother. No other overt supernatural abilities are displayed, though her physical aptitude as an athlete is noted. The ultimate transformation into an angel marks a complete inversion of her original nature, reflecting the story’s theme of overcoming predestined roles through connection and will.