Yasunori Kuroki is a talented oboist who first appears performing the inaugural solo with the R☆S Orchestra. His reserved and phlegmatic nature earns him the description of "samurai-like" from fellow orchestra members. He develops feelings for Megumi Noda, drawn to her perceived purity and simplicity, though learning of her relationship with Shinichi Chiaki distracts him; he maintains friendships with both and later studies abroad in France alongside them.

In France, Kuroki struggles significantly with language, culture, and social adaptation, isolating him and hindering connection. His quiet, awkward disposition leads fellow conservatoire student Tanya to nickname him "Glauque" (meaning dark, depressing, or greenish-blue), critiquing his perceived gloom. Their relationship evolves from friction to mutual understanding, with Tanya eventually becoming his piano accompanist.

Professionally, Kuroki joins the Roux-Marlet Orchestra under Chiaki's direction. His deep dedication to the oboe manifests in meticulous practices like handcrafting his reeds, reflecting both technical commitment and affection for the instrument. His playing style exhibits sensitivity and underlying strength, mirroring his honest, unpretentious personality.

Kuroki's journey culminates in a romantic relationship with Tanya. By the series' conclusion, he proposes, and they become an official couple, marking significant evolution from his earlier social struggles and emotional setbacks.