Kintarō Masaka is the devoted protector and romantic partner of Makoto Onodera, young chairman of Onodera Academy. Their bond stems from a deep-rooted childhood friendship that blossomed into romance and mutual protection. Kintarō serves as Makoto’s personal bodyguard, shielding him from threats driven by a contentious clause in the late principal’s will—a clause encouraging staff to coerce Makoto for control of the academy.

He displays extraordinary combat prowess and agility, deploying acrobatic maneuvers to intercept Makoto’s harassers. His signature "Embarrassment Finisher" (Chissatsu Porori Otoshi) neutralizes foes through extreme humiliation, often using his distinctive axe Masao. Kintarō also counters adversaries with verbal affirmations about authentic emotional bonds.

Trained in mountainous regions, his resilience complements his roles as a university student and Onodera Academy janitor—the latter ensuring constant proximity to Makoto. Kintarō’s unwavering loyalty manifests through vigilant readiness to confront any danger, declaring himself perpetually prepared to defend his partner.

Escalating conflicts with rivals like the Kawakara Branch School deepen their relationship. These adversaries orchestrate sophisticated humiliation traps targeting both. When captured and coerced himself, Kintarō witnesses Makoto’s defiant intervention—a role reversal underscoring their interdependence and reinforcing Kintarō’s conviction that genuine bonds conquer manipulation.

Kintarō’s blend of blunt honesty and occasional naiveté sparks humor amid crises. He affectionately calls Makoto "Makocchan," reflecting their intimacy beyond duty. His protection extends beyond physical safety to safeguarding Makoto’s dignity against systematic harassment, cementing his identity as Makoto’s all-encompassing guardian.