Buju emerges in the post-apocalyptic aftermath of the Overfiend's cataclysmic restructuring, initially a violent marauder engaging in rampant pillaging and sexual violence that mirrors the brutal chaos under cybernetic emperor Caesar's tyranny. As one of the enslaved demon beasts, his specific origins remain undefined. His trajectory shifts upon encountering the infant Lord of Chaos, the Kyo-Ō, born as nemesis to the slumbering Overfiend. Transitioning from self-serving raider to the Kyo-Ō's guardian, Buju embarks on a perilous journey toward Osaka to confront the Chōjin. This quest forces an alliance with other surviving demon beasts—Gashim, Ruddle, and Idaten—spared by the Kyo-Ō's Light of Judgment at Caesar's palace.

A complex relationship with Caesar's daughter Alector becomes pivotal. Despite his initial brutality and enmity stemming from opposition to her father's regime, Alector's profound compassion and capacity to forgive forge a bond that evolves into a central romantic storyline. This connection influences Buju's perspective, intertwining his personal redemption with the cosmic conflict. His journey alongside the Kyo-Ō and companions signifies a search for purpose beyond survival or domination. Though his earlier actions anchor him in moral ambiguity, his commitment to protecting the infant Lord of Chaos and evolving bond with Alector signal a shift toward seeking meaning and redemption. Operating within the narrative's warring factions and deities, his actions directly contribute to the overarching battle between the Overfiend and the rising Lord of Chaos.