Sousuke Ajino, once a celebrated pianist, saw his career end abruptly after a car accident left his left hand permanently injured and claimed his fiancée’s life. Before the tragedy, his unique playing style prompted the crafting of a custom piano with weighted keys, later discarded in a forest as he withdrew from music.

Post-accident, he became a strict elementary school music teacher, feared by students as "Ajino the Deathbringer." His disengagement faded upon encountering Kai Ichinose, a prodigy capable of playing the forsaken piano. This discovery rekindled his purpose, driving him to mentor Kai and secure a professorship at Kiriyama Music Conservatory to nurture the boy’s talent.

Domestically acclaimed in youth for winning top Japanese competitions, he faltered in the International Chopin Competition’s preliminaries. His performance still captivated conductor Jean-Jacques Theroux, sparking a professional rift. A longstanding rivalry with Shuhei Amamiya’s father, a fellow pianist, shaped his resolve to guide Kai outside traditional elitist frameworks.

He sports medium-length black hair, black eyes, and a signature outfit: white shirt, green trousers and tie, and black jacket. His teaching philosophy prioritizes emotional resonance over technical precision, underscoring music as a conduit for human connection.

Across manga, film, and anime adaptations, his journey traces a shift from jaded isolation to committed mentorship, fueled by Kai’s promise. The 2024 spin-off *Totonō Oto: Mō Hitotsu no Piano no Mori* expands the series’ world, though his involvement remains unspecified.