[2] His first main lead starring role was in the tokusatsu television series Madan Senki Ryukendo in 2006, which was a major breakthrough and made him rise to worldwide fame, and is also considered to be his best and most memorable performance to date.
[2] In 2008, he was selected from an audition of 500 actors to play the male lead against the heroine in the NHK Asadora Dandan.
His other notable roles are in the movie Parazoku: Parapara ja Naika (2006) and the television series Hanchō.
[7][8][9] Yamaguchi also continues to maintain a great friendship with Gen & Kouhei Kuroda, who were his co-stars from Madan Senki Ryukendo and played Fudou and Koichi in the show respectively.
[10][11][12] Yamaguchi is a painter and craftsman by hobby, often sharing his creations through social media accounts.