When he thinks a cute girl's come over to talk to him, all she'll ask about is Tsukki
Yamaguchi is a pretty shy person who relies on others. Though he is generally a nice person, he tends to snicker along or join in with Tsukishima whenever he's mocking others. He is hardworking, as shown when he sought for extra training on his own, and how he continued practicing outside of the team after seeing how weak he was compared to his other teammates.
(Source: Haikyuu!! Wiki)