Sousuke Ajino was an internationally celebrated concert pianist whose career ended abruptly in a car accident. The incident caused permanent damage to his left hand and claimed the life of his fiancée. Before the accident, his exceptional talent prompted the creation of a unique custom grand piano with unusually heavy keys, designed specifically for his playing style; only he could fully utilize it.

Forced to abandon performance after the accident, Ajino sold his custom piano. The instrument eventually found its way to the Morinohata red-light district forest. Ajino turned to music education, initially teaching at the university level. However, he struggled to connect with students whose musical interpretations failed to engage him, leading to his resignation.

He later discovered his former piano deteriorated and unplayable in the Morinohata forest. Unable to leave the area, he accepted a position as music teacher at Moriwaki Elementary School. His detached and melancholic demeanor earned him the nicknames "Funeral Ajino" or "Ajino the Deathbringer" among students.

His life transformed upon encountering Kai Ichinose, a young boy who could play the abandoned forest piano. Recognizing Kai's innate talent, Ajino became his mentor and surrogate father figure. This relationship marked a turning point, rekindling Ajino's passion for music through teaching. He dedicated himself to nurturing Kai's abilities, focusing on building technical foundations while preserving his unique artistic expression.

Ajino guided Kai toward competing in the International Chopin Piano Competition in Warsaw, viewing it as a path to liberation from Kai's challenging background. His coaching emphasized artistic integrity and emotional connection over technical perfection or competitive success. Through mentoring Kai, Ajino moved from disillusionment to renewed purpose, finding fulfillment in facilitating the boy's growth and eventual international recognition.

He maintained a reserved personality but demonstrated deep commitment to his students' development, particularly Kai's. His approach involved analytical rigor and high standards, yet he remained protective of Kai's individuality and emotional well-being. This journey allowed Ajino to reconcile with his past, transforming his loss into a foundation for guiding the next generation of musicians.