Hiyu Yamakoshi began his motorsport journey in karting, securing a third-place finish in the 2020 IAME Series Japan's X30 Junior class. Transitioning to single-seaters, he debuted in the 2023 Formula 4 UAE Championship with Pinnacle VAR, later competing in both the French and Spanish F4 Championships the same year. In 2024, Yamakoshi joined Van Amersfoort Racing for the Italian F4 Championship, achieving two victories and seven podiums, culminating in a third-place overall finish. He also participated in the Euro 4 Championship, securing fourth in the standings. In 2025, Yamakoshi is set to advance to the Formula Regional European Championship, continuing his collaboration with Van Amersfoort Racing.