|Date of birth||6 October 1990|
|Place of birth||Nabari, Mie, Japan|
|Height||1.73 m (5 ft 8 in)|
|Playing position||Defensive midfielder|
* Senior club appearances and goals counted for the domestic league only and correct as of 24 December 2018|
‡ National team caps and goals correct as of 2 July 2018
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.
Cerezo Osaka & Japanese National Team
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 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.
- As of 19 February 2019
|Cerezo Osaka||2009||J2 League||3||0||0||0||–||–||–||3||0|
1Includes J2 Play-offs.
- As of 2 July 2018
- Scores and results list Japan's goal tally first.
|1.||5 August 2015||Wuhan Sports Center Stadium, Wuhan, China||South Korea||1–1||1–1||2015 EAFF East Asian Cup|
|2.||6 October 2016||Saitama Stadium 2002, Saitama, Japan||Iraq||2–1||2–1||2018 FIFA World Cup qualification|
- "National Team Squad". jfa.or.jp. Japan Football Association. Retrieved 15 January 2014.
- "Stats Centre: Hotaru Yamaguchi Facts". Guardian.co.uk. Archived from the original on 1 October 2012. Retrieved 13 January 2010.
- "96 verpflichtet japanischen Nationalspieler Yamaguchi". Retrieved 22 December 2015.
- "World Cup 2018: All the confirmed squads for this summer's finals in Russia".
- Nippon Sports Kikaku Publishing inc./日本スポーツ企画出版社, "2017 J1&J2&J3選手名鑑 (NSK MOOK)", 8 February 2017, Japan, ISBN 978-4905411420 (p. 145 out of 289)
- Japan National Football Team Database(in Japanese)
- "Yamaguchi, Hotaru". National Football Teams. Retrieved 30 January 2017.