Sousuke Ajino was a celebrated Japanese pianist destined for global recognition. He owned a custom grand piano with exceptionally heavy keys, crafted solely for him, which produced extraordinary sound under his touch. A devastating car accident abruptly ended his promising career, injuring his left hand and claiming his fiancée's life. Overwhelmed by despair, he sold his unique piano to a Morinohata district nightclub and abandoned performing.

Recovering partial use of his left hand but unable to meet professional demands, he initially taught at a music university but found few students whose interpretations engaged him. A decade later, he resigned and traveled to find his former piano, discovering it ruined and unplayable in the Morinohata forest. Unable to depart, he became the local elementary school music teacher. His stern presence and unhurried manner earned him the student nickname "Funeral Ajino."

Three years into teaching, he met Ichinose Kai, a student claiming to play a forest piano. Recognizing Kai's innate talent upon hearing him play the deteriorated instrument, Ajino became his dedicated mentor and surrogate father. He committed to training Kai, eventually becoming his legal guardian to offer stability and opportunity despite Kai's background in a red-light district. Ajino focused intensely on preparing Kai for the International Chopin Piano Competition in Warsaw, seeing it as Kai's path to transcend his circumstances through music.

His mentorship extended beyond technique, emphasizing emotional expression and musical individuality. During Kai's competition run, Kai used his prize money to fund surgery attempting to restore function to Ajino's injured hand. Ajino initially hesitated, content as a teacher, but accepted after understanding Kai's wish for him to return to performing, aspiring for them to play as equals. Post-surgery rehabilitation involved Kai helping Ajino retrain his left hand, symbolizing a reversal of their roles.

Following Kai's competition victory, Ajino resumed public piano performance. He and Kai performed a joint recital, marking their relationship as musical peers. Former students, colleagues, and residents from Kai's community attended, reflecting Ajino's integration into Kai's life and his rediscovered purpose in music.