Shūhei Amamiya hails from a wealthy family with a distinguished musical heritage; his father is a renowned pianist. Born into this legacy, formal piano training commenced at age four, grooming him to uphold family expectations. Rigorous daily practice forged him into a technically proficient virtuoso. Yet, his playing initially lacked emotional depth and personal expression, the piano feeling more like an obligation than a source of joy.

Transferring to Moriwaki Elementary School brought an encounter with Kai Ichinose. Class bullies dared him to play a dilapidated piano in a nearby forest. He failed to produce sound, but witnessed Kai play the same instrument with remarkable natural ability. This sparked a complex blend of admiration and envy within him, leading to a friendship rooted in music. He saw Kai as both a significant rival and an important friend, often expressing concern indirectly.

His character evolved significantly through this relationship. Initially shy and cautious, interactions with Kai gradually fostered greater assertiveness and willingness to take risks. Maturing, he began doubting his own musical identity, contrasting his technically precise but emotionally restrained approach against Kai's instinctive passion. This internal conflict manifested in emotional outbursts, snapping at Kai or displaying genuine happiness for his achievements.

Years later, he returned to Tokyo intending to reconnect with Kai. Their reunion occurred unexpectedly when he recognized Kai's distinctive piano playing style at a club, where Kai was cross-dressing under the alias "Maria." During a critical performance moment, he helped Kai regain focus by coughing to remind him of the forest piano, enabling Kai's success. This act demonstrated their enduring, if complicated, bond.

At the International Chopin Piano Competition in Warsaw, their dynamic evolved further. He maintained consistent composure during performances but experienced frustration over Kai's near-breakdown in preliminaries and subsequent recovery. Witnessing other competitors, particularly Wei Pang whose style mimicked Ajino's, intensified his reflections on artistic authenticity versus technical replication. His journey culminated in a transition from viewing Kai through envy and rivalry toward a more supportive friendship. This shift reflected his growth in reconciling family expectations with his own musical identity, acknowledging Kai's influence on his development as a pianist and individual.