Age 21 boxer started his career on November 1992 building a record of 39-2-2 over 13 years, last fighting 0 ago in July 2006. Koshimoto's longest KO streak is 3 fights long out of his 43 pro career fights.
Koshimoto proved he was made for the pro ranks in his debut against Masatoshi Fujioka, becoming the first person in Fujioka's 0 fights to stop him. The fight ended in round 1 of 4. Koshimoto's rise in boxing continued with 22 fights against fighters such as Shinya Kiuchi, Atsushi Hagiwara and Junichi Nakamura. He had a mixed start to his career but mostly successful so far.
On November 4th, 1996, Koshimoto went into action again and beat Atsushi Tamaki taking the winning record to 15 wins. Tamaki was stopped in the 8th round via TKO crowning Koshimoto as the first person to stop this opponent. Koshimoto's win streak of 15 rose to 19 following 4 wins against boxers such as Atsushi Hagiwara, Junichi Nakamura, Toshikage Kimura and 1 other.
On December 6th, 1998, Koshimoto went into action again and beat Jun Tanigawa taking the winning record to 20 wins. Jun Tanigawa was Koshimoto's next opponent of his career in 1998. The fight was scheduled for 10 and Koshimoto was the first person to go the distance with Tanigawa where the fight ended in a win for Koshimoto. 3 wins followed where Koshimoto went on to be the 2nd person to stop Junichi Nakamura (Round 7 TKO), 5th person to stop Suk-hwi Cho (Round 4 TKO) and 5th person to stop Dodong Basalo.
Freddie Norwood was next in line for Koshimoto where unfortunately, he was defeated on January 30th, 2000 taking his record to 23-1-2. Freddie Norwood became the first person to stop Koshimoto. The win came via KO in the 9th round of a 12 round bout. Koshimoto's win streak of 23 rose to 38 following 15 great wins, becoming the 2nd person to go the distance with Saengsi Por chaiwat, 2nd person to defeat Seung-kon Chae and 5th person to go the distance with Thongcharoen Suwanasil.
Pushing his career further, Koshimoto fought In-jin Chi on January 29th, 2006 adding to his winning record. In 2006 Koshimoto fought his next opponent in In-jin Chi. A challenging 12 round fight that ended in Koshimoto's favour as the judges awarded Koshimoto the SD victory. Koshimoto was the 2nd person to defeat Chi.
The next defeat of Koshimoto's career came against Rodolfo Lopez on July 30th, 2006. This took his career record to 39-2-2. Lopez turned out to be too much for Koshimoto stopping him in the 7th. Showing that the time was right for Koshimoto to call it a day and retire.