Rock Vulcan is the director of the Gaist Crusher Garrison (GCG), a global organization focused on researching and combating the metallic creatures called Gaist. He exhibits strong leadership, balancing a friendly, approachable nature with serious professionalism in critical moments. His appearance features spiked dark hair, a small goatee, red rectangular eyes, and distinctive downward-pointing eyebrows. He typically wears a black shirt and pants beneath a light blue jacket with orange lining, along with light-grey boots and bronze shoulder plates.

Nine years before the main events, Vulcan served as an active Gaist Crusher on the organization's founding team. His crusher career ended permanently due to the Zeus Incident, which caused him to lose the ability to activate Gaist Gear, specialized armor derived from the energy-rich metal Gaimetal. This incident also indirectly sparked a major conflict: antagonist Izuna Kokuyou held a deep grudge against Vulcan, brainwashed by the hostile Erasers organization seeking Gaist technology for world domination, into believing Vulcan caused his sister's death.

Within the GCG, Vulcan acts as a mentor figure, offering strategic guidance and operational oversight. His extensive field experience directly informs his decisions, especially in coordinating responses to Gaist threats and managing younger Gaist Crushers like Rekka Shirogane. The resolution of Izuna's storyline involves uncovering the brainwashing and the truth about his sister's fate, enabling Vulcan to reconcile with him. Following this, Izuna joins the GCG as an ally.

Vulcan's background as a former field operative who transitioned into leadership underscores his commitment to protecting humanity from Gaist incursions.