He is the shortest member of the team, standing at 1.60 cm. Despite his small stature, he has a strong and firm build. His hair is dark brown and he usually combs it upwards in an attempt to increase his height and a lighter lock of hair falls over his forehead. On his arms and legs he always has marks of blows or bruises from the constant practices he does to improve his supports in the blocks and to be able to help his teammates when they are in trouble in the games. His eyes are brown and slanted. He likes to wear brightly colored shirts with ostentatious messages on the back or chest such as "One Man Army".

Yū is a very energetic and temperamental boy. His hyperactive nature and wild way of acting make it very difficult for him to stay still or quiet for long in one place. He acts before he thinks—when he loses control and gets angry about something, he can resort to violence—and usually has to face the consequences of his actions. He is also quite relaxed in several aspects, such as facing the consequences of his actions, often due to the aforementioned reasons. He is very considerate of the feelings and insecurities that his friends may have. Yū is only shy and quiet when he meets or tries to talk to girls he's meeting for the first time. He is extremely impatient and impulsive, as Tanaka says "(...) He just gets too excited for his own good (...)". He doesn't filter what he says; whatever goes through his head comes out of his mouth, which is why many reprimand him, saying that he is "very sincere".

Even though he's such a noisy person, his attitude changes drastically when he plays, becoming quiet, calm, and serious, completely focused on every move he makes. He always does everything he can to help others and get them out of their obstacles during the game. He doesn't think twice if he needs to throw himself to the ground to catch a ball. He gives his energy completely until the game is over and always encourages others not to give up. For that very reason, the other members of the team respect him very much and know that he is a key part of the team. He can help lift the spirits of his team in just a few words, as has happened many times.

His/Her favorite food is: Garagari-kun (soda flavor). Her hair is exactly 10 cm long. When asked what his current concern was, he replied: "Nothing!" When Kageyama asked him why he had joined Karasuno—believing it was because of the admired coach Ukai, who was often talked about for his effective training methods—he replied: "Because I like the girls' uniform. The boys' uniform isn't gray or brown, but completely black, and it's close to my house. I didn't have to think about it!" During their first training camp, Hinata didn't recognize him and mistook him for a child's ghost, as he had wet hair and was ten centimeters shorter than usual. The first time he met Yachi, he couldn't talk to her because of his shyness around girls, but she felt intimidated by his intense gaze. He is very bad at studying, and one of his worst subjects is contemporary literature. One of his ways of receiving the ball—doing a somersault to get to his feet—is called "Rolling Thunder," and he shouts it while performing the move. It's very embarrassing when someone compliments your skills too much, especially in the cases of Hinata and Tanaka, and you don't know what to say in response. The other members of the team describe him as "a cool person" and also "a wild guy." So when he told Suga that "He definitely became cooler," Suga replied: "It's good to hear that, especially coming from you." When they call him a savage, they compare him to Asahi, who has the appearance of an adult, but is the complete opposite. As a libero, he always makes sure to cheer up his team with words of encouragement or actions, such as in matches where they see their opponents for the first time and feel intimidated; Nishinoya always does something to calm the tension. He also encourages them when they are exhausted and have low morale. It

(To Asahi, during their fight) "Don't you dare give up on serves I've worked so hard to receive! I'm a libero, a vital part of the team's formation! And even with that, scoring points is impossible for me... I'm not allowed to attack. I don't intend to blame you, no matter how many times the ball doesn't go over, but simply accepting defeat so selfishly... That's something I can't forgive." (To himself, while supporting Asahi) "The thickness of my hand is 2 cm. Probably smaller than most kids my age... But those two centimeters are the difference between the ground and the ball, the lifeline of the Ace!" (To give a "sermon" to his teammates) "Kageyama, Tsukishima, Yamaguchi, come here! I'm going to give you a sermon! Get down! I mean... Sit down! Get in my line of sight!" (To the team before the second half against Datekougyou) "Very well! There's no reason to be scared. You guys, just keep looking ahead. I'll watch your backs even if it means giving my life for it!" (To Hinata) "After practice, I'll treat you to a Garigari-kun ice cream because I'm... Your senpai!" (To Hinata) "In a height battle in volleyball, the libero might be the only position where a small player can thrive, even so I'm not a libero because of my height, even if I were two meters tall I would still play as a libero. Even if you can't hit the ball, even if you can't block it... If the ball doesn't touch the ground, then you can't lose in volleyball, and the one who's best at ensuring that is the libero." (To Asahi) "Ask me for a pass, As!"