Matsumoto Yamaga FC
Koyamatsu made his official debut for Nagoya Grampus in the J. League Division 1 on 7 March 2015 (JST) against Matsumoto Yamaga FC by scoring a goal, which was his premiere goal as a J League football player as well. He also started the match against Ventforet Kofu in Yamanashi Chuo Bank Stadium in Kofu, Japan on 14 March. However, he was subbed out in the 70th minute replaced by Kengo Kawamata, then Koyamatsu and his club lost the match 1-0.