On April 22, 2012, Osawa fought in the quarterfinals of the Krush Super Featherweight tournament, being scheduled to fight Yuya Yamato. He won the fight by unanimous decision, and further beat Makoto Morishige by a first-round TKO in the semifinals. These two wins set up the fight with Katsuya Goto, the other tournament finalist, Krush 19.[2]
After winning an extra round split decision against Katsuya Goto in the tournament finals, Shimano earned the chance to fight Hirotaka Urabe for the Krush Super Featherweight title, at Krush 20. Urabe won the fight by a first-round knockout, dropping Shimano with a spinning back kick.[3]
Later Super Featherweight career
After his failed title bid, Osawa was scheduled to fight Yuji Takeuchi at Krush 23. He lost the fight by a third-round knockout.[4]
Osawa was then scheduled to fight Koya Urabe at Krush 27. The fight would end in a disqualification win for Osawa, as Urabe landed an illegal punch as the referee was separating the two from a clinch entanglement. The two were immediately scheduled to fight a rematch at Krush 29. Urabe won the rematch by unanimous decision.[5]
Osawa bounced back from these two losses with back-to-back victories over Keisuke Nakamura at Krush 33 by unanimous decision[6] and Kotaro Shimano at Krush 36 by majority decision.[7] This was followed by back-to-back losses by unanimous decision to Tomohiro Kitai at Krush 39[8] and Toshi at Krush 41.[9]
Following an unbeaten streak of four fights, Osawa was scheduled to make his K-1 debut on July 4, 2015, in a rematch with Kotaro Shimano. As the fight ended in a draw, the two were scheduled to fight a rematch at K-1 World GP 2015: The Championship.[10] Osawa won the fight by unanimous decision.[11] Following a 3–2 run, which ended in a decision loss to Masanobu Goshu,[12] Osawa moved up in weight to lightweight.
Lightweight career
Title fights
He was scheduled to make his lightweight debut against Junpei Aotsu at Krush 83.[13] He would win this, as well as his next two fights against Kyoshiro and Bazooka Koki by unanimous decision.[14] This three fight winning streak earned Osawa the chance to fight Gonnapar Weerasakreck for the Krush Lightweight title.[15] Gonnapar won the fight by unanimous decision.[16]
After losing to Gonnapar, Osawa participated in the 2018 K-1 Lightweight Grand Prix. He won a majority decision against Wei Liu in the quarterfinals, and beat Kyoshiro by a second-round TKO in the semifinals. Osawa fought Kenta Hayashi in the finals, and lost the fight by a third-round TKO.[17]
Continued lightweight career
At K-1: K'Festa 2, Osawa was scheduled to fight Yuto Shinohara.[18] Shinohara won the fight by unanimous decision.[19]
Osawa rebounded with two consecutive victories over Yuzuki Satomi and Zhiwei Wang. He beat Satomi by unanimous decision,[20] and was awarded a DQ win over Wang, after he Wang landed an illegal knee.[21]
He was scheduled to fight a rematch with Yuto Shinohara in December 2019, but had to withdraw after suffering an injury in training.[22]
At Krush 114, Osawa was scheduled to fight Hikaru Hasumi. Hasumi won the fight by TKO, after knocking Osawa down three times in the second round.[23] He was then scheduled to fight Shuji Kawarada at K-1:Winter's Crucial Bout,[24] and lost by split decision.[25]
Osawa snapped the two-fight losing streak with an extra round unanimous decision against Shinichiro Kawasaki at Krush 123.[26]
Osawa was scheduled to face Hiroki at K-1 World GP 2021 Japan on December 4, 2021.[29] He won the fight by unanimous decision.[30]
Krush lightweight champion
Osawa challenged the reigning Krush Lightweight championShuji Kawarada at Krush 136 on April 30, 2022, in what was Kawarada's first title defense.[31] He won the fight by unanimous decision, with scores of 30–28, 30–28 and 30–27.[32]
Osawa faced the 2020 True4U bantamweight tournament winner Dansiam Ayothayafightgym at K-1 World GP 2022 in Fukuoka on August 11, 2022.[33] He won the fight by unanimous decision, with scores of 30–27, 30–28 and 29–28.[34]
Osawa made his first Krush Lightweight title defense against Yuzuki Satomi at Krush 145 on January 21, 2023.[35] He retained his title by unanimous decision, with two scorecards of 30–28 and one scorecard of 29–28.[36] The result was changed into a no contest on January 29, 2023, as Osawa scored the sole knockdown of the fight off of an illegal kick catch.[37] An immediate rematch was scheduled to take place at Krush 150 on June 16, 2023.[38] Osawa lost the title by majority decision, with two judges awarding Satomi a 30–29 scorecard, while the third judge scored the contest as an even 29–29 draw.[39]
Osawa faced Hisaki Higashimoto at K-1 World GP 2023 on July 17, 2023. He won the fight by unanimous decision.[40]
For the Krush Lightweight Championship. Originally a unanimous decision win for Osawa turned into a no contest after review due to an illegal kick catch leading to a knockdown.