In May 2018 he was named in Japan’s preliminary squad for the 2018 FIFA World Cup in Russia.

On 21 December 2015, Hannover 96 announced that they signed Yamaguchi. Yamaguchi played for Hannover 96 in 2016, however returned to Cerezo Osaka mid-season.

In July 2013, Yamaguchi received his first callup to the senior Japan side by Alberto Zaccheroni for the 2013 EAFF East Asian Cup, where he played in all three matches and was named tournament MVP.

Yamaguchi began to receive substantial playing time with Cerezo in 2011, scoring his first league goal on Matchday 24 against Urawa Reds. He also continued to represent Japan under Takashi Sekizuka in qualification for the 2012 Summer Olympics. He followed up by winning a regular position in the Cerezo side in 2012, combining with Takahiro Ogihara in central midfield for both club and country, being named to the Under-23 team representing Japan at the 2012 Summer Olympics, contributing to a fourth-place finish at the tournament. The addition of Fábio Simplício resulted in Yamaguchi being increasingly deployed as an attacking midfielder toward the latter part of the season, which he finished with 30 appearances.

Along with academy teammate Yusuke Maruhashi, Yamaguchi was promoted to the senior team in 2009, spending three months of the season training with the Palmeiras Under-21 academy. He was named to the Japan Under-21 team in his second season and played in all of the matches in a gold medal campaign at the 2010 Asian Games in Guangzhou.

Yamaguchi began playing football in the third grade, playing mostly as an attacking midfielder. Upon entering junior high, he participated in trials with the Cerezo Osaka, Gamba Osaka and Kyoto Purple Sanga youth academies and ultimately joined the Cerezo Under-15 team, from whom he received an invitation on the spot. He enjoyed steady progress at the club, being selected to be part of the first entering class of the Japan Football Association Elite Program at the end of his first year. In 2006 Yamaguchi was promoted to the Cerezo Under-18 team, which later won the JFA Prince League U-18 in the 2008 season, in which he served as captain and was named league MVP.

Hotaru Yamaguchi (山口 蛍 , Yamaguchi Hotaru, born 6 October 1990) is a Japanese footballer who plays as a midfielder for Vissel Kobe. He is also a member of the Japanese national team.