Kozuka was born in
Mitsuke, Niigata. He played junior football for Mitsuke FC and Nagaoka Junior Youth FC in the Hokushin'etsu Youth League while attending Mitsuke Minami Junior High School, before being offered a spot at Teikyo Nagaoka High School on a football scholarship. Kozuka joined
Albirex Niigata as an apprentice professional in 2012. 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. His first J. League appearance was in the 2–1 away win over Tokushima Vortis on 26 April 2014. On 8 July 2014, Kozuka joined
Japan Football League side
Renofa Yamaguchi on loan until December. He scored his first goal for Rnofa against
Sony Sendai on 2 August. 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. On 21 June 2024, he was traded with
Peter Makrillos and moved to
Seoul E-Land FC. == International career ==