B't X is a combat-designed mechanical artificial life form, classified as a kirin-type B't with bull-like horns and a metallic body. Once the Machine Empire's most powerful B't, he was decommissioned and abandoned in a junkyard. His reactivation triggers when Teppei Takamiya's blood contacts his damaged frame during an Empire assault, forging a life-sustaining bond through the BreakHeart device. Initially arrogant and dismissive of Teppei as weak, X prioritizes self-preservation over collaboration, fueling early conflict.

Critical damage from Metalface leads to X's resurrection by Spirit General Hokuto and his B't Max. This reconstruction unlocks his dormant wings for high-speed flight and the "Prism of Aura" ability—a multi-spectrum light-based offensive and defensive power. The near-death experience cements X's unwavering loyalty to Teppei, transforming their dynamic into mutual devotion.

Specializing in aerial combat, X jousts with enemy B'ts. His Guard System shields Teppei from environmental hazards like vacuum or extreme heat, requiring sustained physical contact. Teppei's "Battle Gear" command activates protective armor generated by X, enhancing their synergy. Their signature "Break Heart" attack merges Teppei's energy with X's systems.

Symbolizing resilience and redemption, X's early physical deterioration—a loose leg joint—is temporarily mended by Teppei's bandanna, embodying their interdependence. This repair evolves into a bond where Teppei's willpower directly fuels X's strength, foundationalizing their partnership as inseparable "buddies."

In *B't X Neo*, X confronts the Empire's apocalyptic B't Rafaello. His evolution and alliances with former adversaries like the Spirit Generals prove pivotal. While diverging from the manga in its conclusion, the OVA maintains X's centrality in the climax against the Machine Emperor and Rafaello.