Amiboshi (亢宿?) is a Seiryū Celestial Warrior. He is the elder twin brother of Suboshi and was born in Tenryō, San'un Province in Kutō Empire. The true name is Kōtoku Bu (武 亢德, Bu Koutoku?), born under the star Neck (亢). As a Celestial Warrior, Amiboshi is capable of emitting chi through his mouth and channel it through a flute to control the will of others. A skilled flute player, Amiboshi holds the instrument to the left when using his powers, but to the right when he is simply playing the flute. He works as a spy.
Tranquil and reserved, Amiboshi can become single-minded and merciless. Before Miaka arrives in The Universe of Four Gods, he was a kind young man who was determined to judiciously protect his younger brother. Amiboshi first appears while impersonating Chiriko at the orders of Nakago. When discovered, he falls into a river and is believed to be dead. Found by an old couple, Amiboshi pretends that he has amnesia and the couple adopt him as a son, calling him Kaika. He saves Miaka while she is searching for the Shinzahō, but he pretends that he does not recognize her. As the story progresses, he gradually becomes conflicted between aiding the Celestial Warriors of Suzaku and those of Seiryū.
To save his life, Suboshi gives Amiboshi the forgetfulness potion (through a kiss) instead after Amiboshi nearly dies in order to save his life and protect his future. Losing his memory forever, Amiboshi is protected from sharing the same fate as the rest of the Seiryū warriors and becomes the only surviving member the Celestial Warriors of Seiryū. When Suboshi dies by his own weapon in Miaka's world, after following Tamahome, Amiboshi claimed that he felt like a part of him had disappeared. However, a moment later, he retracts this to say that it felt more like a part of him had come back.