Shintaro Yanagi is a childhood friend of Hiroki Kamikura and Kiri Kikyou, forming a close trio during their high school years. Yanagi harbored deep romantic feelings for Kiri, introducing underlying tension into their friendship. Driven by his attachment to her, he committed a significant betrayal: stealing Hiroki's original artwork—a portrait of Kiri—and submitting it as his own entry for a national art contest. This act of artistic plagiarism secured Yanagi the prestigious competition victory while simultaneously fracturing his friendship with Hiroki irreparably. The theft constituted both professional dishonesty and a profound personal violation, as Hiroki had deliberately concealed his own affection for Kiri to avoid interfering with Yanagi's feelings.

Years later, Yanagi resurfaces as an adult, still emotionally entangled in this past conflict. He attempts to resolve his lingering feelings by confessing his affection directly to Kiri. Kiri rejects him, her heart remaining with Hiroki despite their complex history. Following this personal setback, Yanagi displays emotional growth by accepting Kiri's decision gracefully. He shifts into a supportive role, actively encouraging Kiri to honestly express her enduring feelings to Hiroki. This transition from rival to ally marks his primary character development, positioning him to facilitate emotional resolution between the other central characters.