Hotaru Yamaguchi was born on 6 October 1990 in Mie. He came through Cerezo Osaka's youth ranks and developed into one of Japan's senior central midfielders. After a brief loan to Hannover 96 in 2016, he joined Vissel Kobe in 2019.
With Vissel he won the Emperor's Cup in 2017, 2019 and 2024, the J.League Cup in 2017, the Super Cup in 2018 and 2020, and the J1 League in 2023 and 2024. The 2023 season produced 32 J1 matches with 4 goals; 2024 brought 27 J1 matches with 3 goals.
In January 2025 he moved to V-Varen Nagasaki in J2 (7 league matches in 2025). In January 2026 he returned to Vissel Kobe.
For Japan, Yamaguchi has been a senior call-up for many years. He played in the 2022 World Cup qualification campaign.
A 173cm two-footed central midfielder with vision, ball-control and the senior leadership of a multi-trophy-winning Vissel Kobe veteran, Yamaguchi is one of Japan's most decorated central midfielders. He is in the wider 2026 FIFA World Cup squad picture as a senior central midfielder option.