Kohaku is a rather accident-prone angel who has come to Earth in search of the Angel Master, Hisui. After getting trapped in a tree and attacked by a crow, Kohaku is rescued by Shuuichirou, a young doctor. Feeling indebted, Kohaku offers to grant him one wish, but discovers that the kind doctor is already content with his life. Consequently, Kohaku stays with Shuuichirou, hoping to find a way to repay him while inadvertently getting into more troublesome situations.
Angels and demons do not have human genders, so referring to Kohaku as "he" or "she" is incorrect. However, the English translation of the manga opted to use female pronouns for Kohaku.
After Shuuichirou's sudden death, Kohaku falls into a hundred-year sleep, waiting for Shuuichirou to be reincarnated. One hundred years later, the reincarnated Shuuichirou, now named Kudou Shuishirou, passes by the old house, awakening Kohaku. With no memory of Kohaku, their relationship begins anew.
Kohaku is acquainted with several inhabitants of the Spirit World, including Genko, who admire the angel's singing voice. Kohaku comments on Kobato's progress and the consequences of Ioryogi's actions. Ginsei, concerned about Kobato and Ioryogi, starts visiting Kohaku regularly. In the manga's epilogue, Kobato and Kohaku meet for the first time at Genko's shop and sing a song together in front of Ginsei.
In the anime series, Kohaku is introduced early and befriends Kobato. Knowing Kohaku's true nature, Ioryogi frequently asks if there's a way to change Kobato's wish, but Kohaku always responds that nothing can be done. At the end of the series, Kohaku explains Kobato's wish to Fujimoto and assures him that if he and Kobato are meant to be together, they will eventually reunite.
In the latest chapters of Drug&Drop, Kohaku appears when Kazahaya visits Shuuichirou's house for an errand. They quickly become friends and promise to meet again. Though it's not confirmed, Kazahaya and Shuuichirou share the same surname.
(Source: Wikipedia)
