Atsumasa Ijūin emerged as the primary antagonist in the series, commanding the King B-Ders team through the All-Japan B-Daman Championship with calculated ferocity. His early persona radiated ruthless ambition, exemplified by deliberate sabotage of opponents’ B-Daman gear—a cruelty rooted in childhood trauma. Forced to throw a pivotal tennis match against classmate Cerer, he endured relentless bullying that warped his self-worth, hardening him into a tyrant. Psychological scars from this betrayal fueled his cruelty, while stress physically manifested as progressive whitening of his hair.

His combat arsenal featured Three Claws, engineered for blistering drive shots, and the mythically themed König Cerberus, modeled after Hades’ three-headed guardian. The latter’s catastrophic power annihilated the protagonist’s Fighting Phoenix mid-tournament. During the championship finals, a misfired shot injured his finger, forcing disqualification and defeat by Cerer. This loss shattered his hardened exterior, reawakening his inherent kindness and optimism.

Post-defeat, Ijūin renounced his antagonistic legacy, dedicating himself to rigorous training. His King B-Ders teammates mirrored his visual identity with black tank tops, white accents, tactical shoulder pads, and uniform footwear. Their collective arc wove themes of rivalry, redemption, and the corrosive effects of unchecked ambition.

Both manga and anime iterations aligned in depicting his journey, though his endeavors beyond the championship remain unchronicled. No supplementary media expands upon his post-series evolution, anchoring his narrative to the tournament’s confines.