[5] Oshima made her professional debut against Yuki Ono at Shooto 2020 1/26 on January 26, 2020, at the age of 25.

[7] Oshima won the fight by a second-round technical knockout, stopping Ono with punches from the crucifix midway through the round.

[16] Oshima took part in the Jewels Atomweight Grand Prix, organized to crown the new champion, as the title was left vacant following Tomo Maesawa's retirement.

[18] Oshima faced Si Woo Park at Deep Jewels 33 on June 19, 2021, in the semifinals of the grand prix.

[24] Oshima faced Namiko Kawabata in a Super Atomweight bout at Deep Jewels 36 on March 12, 2022.

[27] She won the fight by a first-round technical submission, forcing a referee stoppage with a kimura lock.

[31] She won the fight by a first-round submission, forcing Furuse to tap to an americana just 84 seconds into the opening round.

[33] She won the fight by a third-round submission, as she forced Hong to tap to an armbar 59 seconds into the final round.

[36] Oshima made her second Jewels Atomweight Championship defense against Si Yoon Park at DEEP 115 on September 18, 2023.

[38] Oshima faced Claire Lopez at Rizin Landmark 8 on February 24, 2024, stepping in on a week's notice, as a replacement for the injured Ayaka Hamasaki.