Masaaki Yanagisawa is the karate club captain at Nika High School, also called Goujyu High, mentoring the protagonist Natsuki Kisumi. He possesses notable, superhuman strength within a powerfully built, imposing frame.

His background connects significantly to the elite martial arts-focused Jotoh Academy. Yanagisawa received an invitation to train there but declined, choosing to stay at his current school. This decision rejected Jotoh's philosophy, which he perceived as prioritizing dominance and lethal force. His potential as a fighter was such that his style "trembled everyone" at Jotoh.

Yanagisawa acts as both mentor and protector to Natsuki. He trains her actively, advising on combat strategies like the dangers of Rina Takaoka's joint-locking wrestling. He intervenes physically in critical moments, rescuing Natsuki when she is overpowered by the formidable judo champion Akira Kandori, a former associate from Jotoh. His protective role extends to shielding Natsuki from a sword attack during a confrontation, sustaining an injury.

His core philosophy defines him: Yanagisawa consistently advocates for martial arts as a means of self-improvement and honorable competition, explicitly opposing its use for killing or inflicting unnecessary harm. This belief directly conflicts with Jotoh's ethos and drives his confrontation with Akira Kandori, who embraces Jotoh's pursuit of absolute strength. During their encounter, he states his conviction that martial arts should focus on defeating opponents without destroying them, reinforcing his rejection of Jotoh's path.

His relationship with Akira Kandori involves unresolved personal history. Akira expresses bitterness over his departure from Jotoh, interpreting it as abandonment and a rejection of greater power. She challenges his ideals by targeting his students, aiming to prove Jotoh's methods superior.