Shiina Amamiya, a 17-year-old transfer student at Hakujou Academy, stands 160 cm tall with striking purple hair and violet eyes. Her initial recognition stems from placing second in the London Piano Contest, narrowly behind Haruka Nogizaka. Exhibiting a blood type A personality, she typically radiates self-confidence, directness, and initiative—yet reveals unexpected shyness in romantic scenarios. Though raised in Otaru, Hokkaido, she seldom references her past.

Her passions include piano performance and mastering naginatajutsu, a traditional martial art. Naturally cheerful and sociable, she adapts seamlessly to her new school. The academy's "Performer of the Sunset," a distinguished music teacher, partly motivated her transfer.

Prior encounters with Yuuto Ayase sparked her romantic interest, often leading to comedic mishaps like accidental panty exposures. Despite her usual assertiveness, confessing her feelings triggers internal conflict. Encouraged by friends Mai Asahina and Ryōko Sawamura to pursue Yuuto, she sometimes unintentionally aids his budding relationship with Haruka instead.

Her bond with Haruka balances camaraderie from shared piano history against Shiina’s quiet sense of being perpetually "second best" to Haruka in music and love. Throughout her journey, she navigates unrequited affection but consciously avoids undermining Yuuto and Haruka’s relationship. Ultimately, she accepts Yuuto’s choice, supports their union, and evolves toward emotional maturity—prioritizing his happiness above her own desires.