tadashi Yamaguchi🪼٭★٭˚∘•

He has dark grayish-green hair with a flyaway piece of hair sticking up at the top. He has large eyes with small, amber colored pupils. Yamaguchi is taller than average and has a thin build. This, coupled with his freckles, had caused him to be bullied when he was younger,[3] although he doesn't seem to be bothered by this anymore.

After joining the Karasuno volleyball team during games, Yamaguchi wears Karasuno's black, orange, and white uniform with the number 12 on the back. He also wears knee pads and white volleyball shoes with black accents. Outside of matches and practice, Yamaguchi wears a black gakuran, the Karasuno uniform.

By his third-year of high school, Yamaguchi is shown to have cut his hair to a shorter length. He kept this look after the timeskip.

Yamaguchi is a pretty shy person who relies on others early on, most likely stemmed from being bullied because of his appearance. Despite this, Yamaguchi is generally a nice person but does tend to join Tsukishima in teasing others, mainly Kageyama and Hinata. He does show that he is a loyal friend and a supportive teammate. Yamaguchi can at times be seen defending Tsukishima from things he believes were insults toward his friend.

Originally, Yamaguchi constantly doubted his abilities and had difficulty handling his nerves. It was through hard work and seeking mentorship through Shimada that he was able to better his skills and become more confident. By the time Karasuno had their rematch against Aoba Johsai in the semifinals, Yamaguchi has made exceptional progress in both his gameplay and emotions.Back in elementary school, Yamaguchi was teased for his freckles and overall scrawniness. Once Tsukishima unintentionally saved him from some boys who bullied him by calling them pathetic. Despite thinking that he was included among the ones Tsukishima insulted, Yamaguchi still grew attached to him and looked up to him, he set his goal to become "as cool as him". He is later revealed to want to join a sports club but decided against soccer and basketball because the other players were 'big and scary' and volleyball seemed the safer choice. From this, he and Tsukishima grew to become close friends.

Yamaguchi was with Tsukishima when he attended a Karasuno volleyball match and Tsukishima's brother, Akiteru, was revealed to not be on the team.