Sentarō Miya’s youthful features—light brown hair, bright eyes, and a petite frame—routinely lead strangers to assume he’s a middle school student. This misconception ignites his short fuse, sparking fiery clashes with anyone bold enough to mention his height. Though quick to anger, he wears his heart openly, tearing up easily or flushing crimson in the presence of girls; Satowa Hozuki’s mere proximity once triggered a nosebleed. His thorny rapport with Chika Kudo stems from Chika’s initial jab at his age, fueling their constant bickering.

Family anchors Sentarō’s world. He dotes on his younger sister and makes weekly visits to his grandmother, prioritizing these bonds over school breaks. At meals, he champions yakiniku as a mark of toughness but recoils at green peas and beans, pushing them aside with visible distaste.

In the koto club, he balances a trio with Haru Kasugai and Akari Kobayakawa—their striking height differences (tall, short, tall) draw attention during national contests. His name, Sentarō, weaves meanings of "thousand," "greatness," and "cheerfulness," while "Miya" evokes sacred spaces, layering his identity with cultural resonance.