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. 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.