Kohaku is an angel who comes to Earth in search of the Angel Master, Hisui. This search leads to an accident-prone arrival, becoming trapped in a tree and attacked by a crow before being rescued by the young doctor Shuuichirou Kudou. Feeling indebted, Kohaku wishes to grant a wish but finds the kind doctor satisfied with life, prompting Kohaku to remain by Shuuichirou's side. Kohaku is characterized by a good-natured, warm-hearted, and cheerful personality. This gentle nature allows Kohaku to form a quick bond with the protagonist Kobato Hanato. Within the story, Kohaku serves as a supporting figure who provides guidance and perspective. Kohaku is an acquaintance of the spirit world resident Genko and several other inhabitants, many of whom admire Kohaku's singing voice. Motivated by a desire to repay Shuuichirou and genuine kindness towards others, Kohaku navigates the human world with an accident-prone manner. Kohaku's relationship with Shuuichirou is a central anchor for the character, based on gratitude and affection. Another key relationship is the friendship with Kobato, with whom Kohaku shares the song Ashita Kuru Hi. Kohaku is aware of Kobato's true nature and the stakes of her wish, offering comfort and explanations to characters such as Fujimoto. The angel Ginsei also regularly visits Kohaku. Kohaku retains several supernatural abilities, including the ability to manipulate water and to hear, understand, and communicate with the voices of trees. The character develops through a deepening understanding of human emotions and connections, remaining a steady, reassuring presence throughout the narrative.