Koizumi's journey began in the Japan GT series - GT300 from 2007 to 2010, establishing a foundation for his motorsport career. In 2009 and 2010, he ventured into the Japanese Formula 3 Championship - National Class with C.M.S Motor Sports Project, securing a commendable ninth position in 2009’s championship. The following years, 2011 and 2012, saw him continuing in the Japanese Formula 3 Championship with Hanashima Racing, maintaining a consistent presence in the top ten. Koizumi achieved a significant milestone in 2013 when he participated in the Fuji round of the Asian Le Mans Series - LMP2 with KCMG, clinching the top spot. His prowess in Formula 3 Japan continued in the National Class with Hanashima Racing, earning multiple podiums and a third-place finish in the championship in 2013, followed by a championship win in 2014. In 2022, Koizumi entered the Fanatec GT World Challenge Asia Powered by AWS - GT3 with ABSSA Motorsport, showcasing his adaptability across different series. The same year, he triumphed at the Algarve round of the Michelin Le Mans Cup GT3 class with AF Corse. The year 2023 saw Koizumi's participation in the FIA Endurance Trophy for LMGTE Am Drivers at Fuji and a second-place finish in the Michelin Le Mans Cup GT3 Drivers Championship with AF Corse. Now, as he takes the wheel of the #82 Corvette Z06 GT3.R LMGT3 for TF Sport in the 2024 FIA World Endurance Championship, Koizumi looks forward to the challenges and opportunities that lie ahead.