Suboshi (角宿?) is a Seiryū Celestial Warrior and the younger twin brother of Amiboshi. The true name is Shunkaku Bu (武 俊角, Bu Shunkaku?), born under the star Horn (角). As a Celestial Warrior, he is able to use a secret weapon known as the Ryūseisui, a double meteor bell, and control it with his will alone. He and his brother are also able to communicate with one another by writing messages on their bodies.
In terms of temperament, Suboshi is fierce, impulsive, and stubborn to a fault, unwilling to listen to reason once he becomes determined to do something. He and his brother are extremely close as a result of their losing their parents at a young age and having a tough childhood. Suboshi is particularly devoted to his brother and will not hesitate to kill if it means protecting Amiboshi, even killing fellow Seiryū warrior Tomo without a second thought for this reason alone.
Suboshi falls in love with Yui Hongo, who is the first person aside from his brother to show him any tenderness, when she comforts him after the apparent death of Amiboshi. As a result, he develops a strong hatred for Miaka for supposedly abandoning Yui and jealousy towards Tamahome, whom Yui loves. Believing Tamahome to be responsible for Amiboshi's death, Suboshi murders Tamahome's family for revenge.
Though he is eventually reunited with Amiboshi, Suboshi chooses to administer a potion of forgetfulness to save Amiboshi, who is near death. With his memories completely lost, Amiboshi is saved by his brother from sharing the same fate as the Seiryū warriors. Suboshi later arrives, using Yui's school-uniform's ribbon as a medium, in the real world trying to kill Miaka and Tamahome, but is killed by his own weapon, vanishing shortly afterwards. The ribbon stays in the real world, and Miaka returns it to Yui.