[3] He turned full-time professional with Albirex at the start of the 2013 season and made his first-team debut against Tokushima Vortis in the first round of the Nabisco Cup.
On 8 July 2014, Kozuka joined Japan Football League side Renofa Yamaguchi on loan until December.
[5] He became regular for Renofa, creating a strong attacking partnership with Kazuhito Kishida.
Kozuka impressed at Renofa, and his loan deal was eventually extended to the end of the 2015 season.
On 6 April 2015, in the 3–0 league victory at Fujieda, Kozuka scored a 60-yard goal from the halfway line.