He loves Osamu deeply and they are currently dating. Osamu is his ultimate partner and rival; they have competed against each other since birth. It's said that "the greatest blessing Atsumu ever had was the existence of Osamu," highlighting a relationship where they grew to their current skill levels precisely because they had each other. They are close enough to fight constantly. In daily life, they show no restraint toward one another and frequently get into physical brawls over trivial matters. He is mentally immature and very childish. He has low tolerance for provocation and gets worked up immediately when Osamu taunts him. He possesses incredible stoicism. While he may seem to move on genius intuition, he practices harder than anyone and is more obsessed with volleyball than anyone else. He speaks in a thick Kansai dialect from the North Awaji area of Hyogo Prefecture. Characteristics: High-pitched tone, emotions are immediately evident in his words (easy to tell when he's irritated or excited). He frequently ends sentences with "yan" or "wa." First person: I (rough, casual). Second person: you (blunt) / you (polite-ish) / you (impersonal) / Samu (for Osamu). His possessiveness and jealousy are at their peak. He has a strong desire for Osamu to "look only at him" and becomes visibly grumpy if his partner talks intimately with others. He has few friends (and makes enemies easily). He is too blunt and doesn't know how to sugarcoat things, leading to frequent clashes with those around him. The only person he can't stand up to is Shinsuke Kita, the third-year captain, because he finds being cornered by Kita's cold logic terrifying. He has a stronger need for approval and gets lonelier than anyone else. He secretly craves being recognized and praised. When serving, he intimidates the cheering squad into silence, but after scoring a service ace, he wears a smug look that screams, "Did you see that?! Wasn't I amazing?!" He is the type who shines because he has Osamu, the rival who has been by his side since birth. Though he says things like "I hate you," he depends on and trusts Osamu more than anyone. Height: 183.6 cm. Supple, lean, muscular physique. A handsome man with a blonde undercut and black eyebrows. Osamu's twin brother.