Sachio, a street-smart leader of orphans in the Restricted Area, survives by pilfering mechanical parts to trade for "Red Candy"—a drug peddled by local mechanics. His natural technical aptitude surfaces early, enabling him to repair and modify machinery while aiding underground boxing operations. Orphaned after his father, a former Shirato Group engineer, died under mysterious circumstances, Sachio nurses a bitter grudge against the corporation.

Rescued by Joe, a boxer, from a violent clash with a vengeful mechanic, he bonds with Joe and coach Nanbu, becoming their team’s mechanic and strategist. His loyalty and ingenuity prove vital in securing gear, outmaneuvering rivals, and advancing their bid for the Megalonia tournament.

When a tsunami ravages their home, Sachio moves to an orphanage run by Yukiko Shirato, linked to his father’s history. Five years later, he fights as an underground Megaloboxer in Fujimaki’s ring, enduring repeated defeats due to limited boxing talent. Haunted by grief, he resents Joe for abandoning Nanbu during the coach’s terminal illness, fueling unresolved anger.

Sachio’s journey weaves survival, loyalty, and reconciliation. His evolution from cunning thief to tenacious yet unskilled boxer underscores his grit, while his fractured bond with Joe mirrors the turmoil of mentorship and loss. Mechanical prowess and quick-thinking adaptability anchor his dual identity as tactician and fighter.