Kokuryu serves as the eldest brother within the Three Color Dragons, a trio of siblings acting as warriors for Captain Klaus Daggats' Spiral Palace forces in Grazia. Alongside his sister Hakuryu and younger brother Kouryu, he specializes in Chinese martial arts, their combat style emphasizing cohesive teamwork rooted in these techniques. Recruited into Klaus' organization relatively recently before the main Spiral Palace events, they form part of its international roster of warriors, contributing to the tower's structure as a martial stronghold housing diverse combat arenas. The siblings possess their own designated mini-palace section within the complex, complete with a lake.

Following an encounter with protagonist Taito Masaki in Grazia prior to the palace assault, Hakuryu develops reluctance when Klaus orders the trio to confront Taito. This hesitation introduces a degree of internal conflict or loyalty questioning among the siblings, triggered by their prior interaction. Kokuryu's role remains defined by his membership in this familial warrior group under Klaus Daggats' command.