Reponen, who also played pesäpallo and soccer in his youth , made his international debut at the “FIS Children Grand Prix” in Oberstdorf . He won the Gundersen competition from the middle hill and over four kilometers ahead of his compatriot Waltteri Karhumaa and Lenard Kersting . Around a year later he won the opening competition of the Youth Cup at the same place . Reponen also regularly placed himself on the podium in his subsequent participation in youth competitions. On January 12, 2018, he made his debut in the Continental Cup in Ruka , Germany, but missed the points. The Finnish junior champion from spring 2018 first achieved this in December 2018, when he won four points in Steamboat Springs . In the following two competitions, he finished seventeenth. For the rest of the season, Reponen did not compete in the Continental Cup, so he finished 62nd in the 2018/19 overall standings . At the Nordic Junior World Ski Championships 2019 in Lahti , he was seventeenth in the sprint and 34th in the individual. He finished seventh with the team.