"[2] He made his Koshien debut in the Spring Senbatsu tournament where his team lost 4–1 against Tokai University Sagami Senior High in the first round where Ōno took 3 strikeouts for one earned run in 3+2⁄3 innings.

[4][5] On July 11, 2012, Ono made his second start, this time against the Hanshin Tigers at Koshien Stadium where he would get his first victory after pitching 5+1⁄3 innings, conceding one earned run and 7 hits.

His then career-best 2.52 ERA ranked sixth in the Central League[11] and his six complete games were second only to the seven recorded by the Hanshin Tigers' Shintaro Fujinami.

On March 25, 2016, Ōno was selected as the starting day pitcher against the Hanshin Tigers at Kyocera Dome where he pitched a winning 5-2 game, striking out 3 and walking 2 for 2 earned runs in 7+2⁄3 innings.

[12] Ōno went on to win one more game and lose one for an ERA of 2.66 before April 15 where he was deactivated from the first team roster due to concerns regarding elbow discomfort.

[18] In 2019, Under the guidance of new manager Tsuyoshi Yoda and pitching coach Hideyuki Awano, Ōno found new life returning to the starting day rotation.

[22] Ōno received the Sawamura Award for his performance in the 2020 season, leading the Central League with a 1.82 ERA, 10 complete games, six shutouts, 148+2⁄3 innings and 148 strikeouts.

[23] At the end of the season, and before receiving the Sawamura award, Ōno signed a 3-year, ¥900 million incentive laden deal to remain at the Dragons.

During his university playing days, Ōno had attached a Torakki strap to his mobile phone,[35] however, once he was selected by the Dragons, he promptly removed it.