During the 2020–21 season, he served as an alternate captain and recorded 23 goals and 26 assists in 38 games with Oulun Kärpät's junior team in Finland's top junior league, U20 SM-sarja.

[2] On 15 August 2021, the Hurricanes signed Koivunen to a three-year, entry-level contract.

[3] On 7 March 2024, Koivunen was traded to the Pittsburgh Penguins, along with Michael Bunting, prospect Cruz Lucius, Vasili Ponomaryov and two conditional 2024 draft picks, in exchange for Jake Guentzel and Ty Smith.

[4] Koivunen represented Finland under-18 team at the 2021 IIHF World U18 Championships where he recorded four goals and six assists in seven games.

This biographical article relating to a Finnish ice hockey player is a stub.