[1] Kojima won the Japanese Chess Championship five times, in: 2005, 2006, 2007, 2008, 2010.
In November 2022, Kojima won the Japan Open 2022, where he remained undefeated during the event.
[2] He won the Japan Open 2021 in the previous year, where he was the top-ranked Japanese player.
[3] In July 2023, Kojima finished tied for second in the Japan Chess Classic 2023 alongside Trần Thanh Tú, Koya Matsuyama, and Samuel Song.
[4] As of September 2023, Kojima is one of two active International Masters in Japan, alongside Ryosuke Nanjo.