[2][3] Oka competed at the 2018 Junior Asian Championships where the Japanese team won the silver medal behind China.

[6][7] Then in the first day of event finals, he won the silver medal on the pommel horse behind teammate Takeru Kitazono.

[8][9] Then on the final day, he won the bronze medal in the parallel bars behind Kitazono and China's Yang Haonan.

[18] Oka won the all-around title at the 2023 Asian Championships in an upset over Carlos Yulo.

[22] Oka began the 2024 season at the All-Japan Championships where he won the all-around silver medal behind Daiki Hashimoto.

[23] He then won the all-around title at the 2024 NHK Trophy and earned a place on Japan's 2024 Olympic team.