Sentaro Miya attends Eidai High School as a male student and participates in its koto club. His notably short stature frequently results in him being mistaken for a middle schooler; he has light brown hair and eyes. Sentaro possesses a hot temper that surfaces swiftly when others mention his height, often sparking arguments or confrontations. Despite this quickness to anger, he displays emotional sensitivity and a tendency to cry. He also exhibits distinct weakness around girls, such as developing a bloody nose upon seeing Satowa Hozuki. Within Eidai High's koto club, Sentaro belongs to a trio alongside Haru Kasugai and Akari Kobayakawa. Their physical arrangement follows a "tall-short-tall" pattern: Haru stands as the tallest character in the series, Akari nearly matches Haru's height, and Sentaro occupies the "little guy" position between them. His interactions with Tokise High School's Chika Kudo begin contentiously, marked by arguments primarily ignited when Chika misidentifies Sentaro as a middle school student due to his height. Sentaro favors yakiniku, associating the grilled meat with masculinity and stating "a man should naturally eat it." He dislikes green peas and beans. During school holidays, he engages in physical training, cares for his younger sister, and visits his grandmother regularly—extending these visits beyond holiday periods.