From 2021 season, he will be the assistant coach of
Shonan Bellmare on 14 May 2021. On 1 September 2021, Yamaguchi was appointed as manager of J1 club,
Shonan Bellmare following the retirement of
Bin Ukishima for during 2021 season. After winning his first victory as a manager in the 33rd round against
Yokohama FC. On October 23 at same year, he led the team to remain in the final round of the 38th round against
Gamba Osaka on December 4 at same year. It was decided that he would continue to serve as manager in the 2022 season and in June he was awarded the monthly best manager award. ==Club statistics==