In 2024, Kotaro earned a scholarship at the Honda Racing School Suzuka finishing as runner-up and, while competing as a private entrant, secured 3rd place in the Japanese FIA-F4 Championship.

In 2025, supported by the Honda Racing School Suzuka scholarship, he competed in the Japanese FIA-F4 Championship with HFDP (Honda Formula Dream Project) with B-MAX RACING TEAM. He achieved two pole-to-win victories and a total of five podium finishes, ending the season 4th overall.

In 2026, he continues with HFDP with B-MAX RACING TEAM and will compete in SUPER FORMULA LIGHTS.