He is the father of Teru.
Ginga Densetsu Weed
Kyōshirō tore off Teru's father's ear, as he caught him beating up Teru because his meal was stolen. He was almost killed until Weed interfered. This causes Teru's father to seek revenge on Kyōshirō for what he did to his ear, and turning his own child against him. Therefore, he helps Lecter and Thunder by luring Kyōshirō into a trap.
But when Lecter takes Teru as hostage, he attacks Lecter, having found the courage to protect his son and the shame for mistreating him. He is severely wounded and succumbs to his injuries but not before his son forgives him. He apologizes before he dies, leaving his son to cry over his dead body.
It is the change of heart and death of Teru's father that convinces Kyōshirō to join Weed after witnessing the father's heroic death to protect his son, and made Kyōshirō change Kōta's name back to Teru.