Izuna Kokuyou, whose name is sometimes rendered in English as Obsidian Izuna, is a character from the anime Gaist Crusher and one of the series' main protagonists. He serves as the thunder attribute crusher of the GCG, the organization dedicated to fighting the metallic life-forms known as Gaist. In appearance, he is a teenage boy with gray hair cut to roughly ear length and orange eyes.

His background is defined by an incident from his childhood involving a Gaist, and this past event is the root of the grudge he holds against Rock Vulcan, another crusher. Because of that resentment, Izuna is initially introduced as an enemy of the main crusher team rather than as one of its members. His early actions are driven by this personal grievance, which puts him in conflict with Rock Vulcan and with those aligned with him. Over the course of the story, however, he sets aside this hostility and rejoins the GCG, taking his place among the protagonists as the narrative progresses.

In terms of his role, Izuna is distinguished among the GCG crushers by his thunder attribute, which defines his combat style and the nature of his Gaist Gear. His most significant relationship is with Rock Vulcan, the target of his grudge and the source of his early antagonism, and his character arc centers on resolving that conflict. He also has a younger sister, Honoka Kokuyou, who is connected to his childhood in the broader Gaist Crusher story material. His development follows a clear path from adversary to ally, as he overcomes personal resentment and commits himself to fighting alongside the GCG.

His notable abilities are tied to his identity as a thunder attribute Gaist Crusher, meaning he fights while equipped with Gaist Gear aligned with thunder-based power and engages Gaist directly in combat in the same manner as the other crushers in the series.