[4] His international achievements include winning a bronze medal in the men's individual at the 2014 Asian Games, behind Guo Jianli and Jung Jin-hwa.

[7][8][1] In November 2017 Iwamoto won the 57th Modern Pentathlon All Japan Championship, which was held in the Chiba Prefecture.

[9] Competing in the Modern Pentathlon World Cup, his best achievement in 2018 was sixth place in the competition in Los Angeles in April.

[11] In an interview from April 2020, Iwomoto tells about his sports career so far, explains the competition format of modern pentathlon in detail, and answers questions about his goals for the Tokyo Olympics.

[4] A courtesy visit by Iwamoto to Governor Shioda of the Kagoshima Prefecture ahead of the Olympics attracted enough interest to merit media coverage.