Debut

He made his debut at Pancrase Progress Tour 4, earning a draw against Yoshifumi Ishiki.^[3]

ZST

3 months following his pro debut, he entered ZST's Bantamweight tournament, earning his first victory against Tadayuki Nakamura with what would become his patented rear-naked choke at ZST: Battle Hazard 6.^[4] He followed this up by scoring a unanimous decision victory in the semifinals against Nobuyuki Kanaizuka at ZST: SWAT! 47 ^[5] He met future ZST Flyweight Champion, Seiichiro Ito in the finals, scoring an emphatic submission in just 62 seconds to capture the bantamweight tournament championship at ZST: SWAT! in Face 11 ^[6] Despite winning a tournament only 5 months into his career, he would face a dip in form, going 2-1-3 in his next 6 fights, with his sole victory coming against Shintaro Kubo at VTJ 2nd in June 2013. He started 2014 off with a stoppage loss to future foe Go Kashiwazaki, but strung together a 7-fight unbeaten streak lasting 2 and a half years, earning a rematch with Kashiwazaki - this time for the ZST Bantamweight Championship. His fate would be nearly identical, losing via stoppage in the 2nd round. This would prove to be his final appearance with ZST, finishing with a 8-3-4 record in the promotion (9-3-5, 1NC overall).^[7]

Fighting NEXUS & GLADIATOR

Watanabe would make his Fighting NEXUS debut 3 months following his failed title challenge for the ZST title, kicking off his NEXUS career nearly identical to his ZST debut, a rear-naked choke victory in just 85 seconds. 4 months later he competed under the GLADIATOR banner, scoring a second successive rear-naked choke victory against Yutaka Imamura; a victory which would catapult him to his second title challenge in 12 months. However, he first competed at Fighting NEXUS 9, finishing Jun Ikkyu with a guillotine choke in just 24 seconds. This allowed for a quick turnaround, to face Naritoshi Kakuta for the GLADIATOR Bantamweight Championship. However, once again, Watanabe would come up short, dropping a unanimous decision. He closed out 2017 with a unanimous decision victory of his own, over Kotaro Kazama. This win would spur on a 9-fight unbeaten streak, in which he would capture the vacant Fighting NEXUS Bantamweight Championship in December 2018, and score 2 victories under the DEEP promotion.^[8][9][10]

RIZIN Fighting Federation

With an impressive unbeaten streak stretching back 2 and a half years, Japan's premier MMA promotion, Rizin Fighting Federation announced that Watanabe would be facing rising prospect and UFC veteran, Naoki Inoue on August 9, 2020 at Rizin 22.^[11] Watanabe was defeated at 1:40 of the first round via rear-naked choke.^[12]

On February 16, it was announced that Watanabe would face Takumi Tamaru at Rizin 27 to earn a spot in RIZIN's upcoming Japan Bantamweight Grand Prix, with the winner of the grand prix being expected to face RIZIN Bantamweight Champion, Kyoji Horiguchi in 2022.^[13] Watanabe defeated Tamaru by rear-naked choke in the 2nd round.^[14]

4 days later, RIZIN held a press conference where the drawing for the Grand Prix would occur. Former RIZIN Bantamweight Champion Kai Asakura chose the slot to face Watanabe. They faced each other at Rizin 28 on June 13, 2021 at the Tokyo Dome.^[15][16] Shooto lost the fight by a first-round technical knockout.^[17]

Watanabe was scheduled to face Kuya Ito on October 10, 2021 at Rizin Landmark Vol.1.^[18] Ito later withdrew from his bout with Watanabe due to COVID-19 protocols, and was replaced by Nobutaka Naito.^[19] He won the bout after choking Naito unconscious via brabo choke in the first round.^[20]

Watanabe was booked to face Takuma Sudo on April 16, 2022 at Rizin Trigger 3.^[21] He lost the fight by split decision.^[22]

DEEP

Watanabe faced Takuma Uchiyama at Deep 108 Impact on July 10, 2022. He won the bout by unanimous decision.^[23]

Watanabe faced Rikiya Matsuzawa on February 11, 2023 at DEEP 112, losing the bout via TKO stoppage 27 seconds into the bout.^[24]