Ogasawara made his professional debut in July 2017 against Shoyo Yuasa, during the REBELS×IT’S SHOWTIME crossover event.
[3] After a KO victory in Thailand a month later, Eisaku went on a six fight winning streak, beating Tatakau Pastry,[4] Naoya Yajima,[5] Yasuhito Furuta,[6] Yosuke Kafuji,[7][8] Dynamo Puchi,[9] and Kiminori Matsuzaki.
[14] Ogasawara was then scheduled to fight Hong Chunhen,[15] but once again lost by KO, after being dropped three times in the second round.
He beat Rose Tatsuya and Satoshi Katashima by TKO,[17][18] and won decisions against Yasuhito Furuta,[19] Yun Dok Jae[20] and Jockylek GT-gym.
[35] Ogasawara won his next five fights by (T)KO as well, scoring victories over Keisuke Miyamoto,[36] Hiroya Haga,[37] Sung Ji Byun,[38] Wanchalong PK.Saenchai[39] and Hyo Sik Hwang.
[40] Ogasawara was set to fight Franck Gross for the ISKA K-1 rules World Bantamweight title.
[41] After a draw with Ryo Takahashi, Ogasawara fought Dawsakon Mor.Tassanai for the WPMF World Super Bantamweight title.
[46] Eisaku beat Petyaso Dabrunsarakarm by a head kick KO at the Pancrase REBELS Ring 1.
[48] He lost to Yuki Kasahara by TKO, after the ringside doctor stopped the fight in the second round.
He is scheduled to face his brother Yukinori Ogasawara in the final for the inaugural REBELS-RED 55.5 kg title.
[58] Ogasawara was scheduled to face the former DEEP KICK 57.5 kg champion Hiro Yokono in a non-title bout at KNOCK OUT 2021 vol.3 on July 18, 2021.
Both the knockout and the knockdown that preceded it were scored it the same manner, by low kick, which Ogasawara had been throwing throughout the bout.
[68] Ogasawara faced the three-weight Lumpinee Boxing Stadium champion Ronachai Tor.Ramintra at KNOCK OUT 2023 SUPER BOUT BLAZE on March 5, 2023.