The narrative unfolds across four distinct acts:
Act I: The Awakening (Episodes 1–4): Ten years after throwing his 2007 Olympic qualifying match to fund his sister Dong-hee's surgery, Dong-man drifts as an exterminator. Ae-ra dumps her cheating boyfriend and discovers her wealthy suitor, Dr. Moo-bin, is already engaged and viewing her as a disposable secret affair. Rescuing each other from emotional humiliation, Dong-man commits to MMA training under Coach Hwang, and Ae-ra resigns to pursue broadcasting.
Act II: The Transition from Friendship to Romance & The Rift (Episodes 5–10): Dong-man achieves rapid knockouts in amateur MMA, while Ae-ra fends off Dong-man's manipulative ex Park Hye-ran. Meanwhile, Joo-man becomes conflicted by wealthy intern Jang Ye-jin, whose innocence reminds him of Seol-hee's past. While Joo-man avoids physical infidelity, his lies of omission deeply hurt Seol-hee. In Episode 10, Dong-man and Ae-ra share a romantic kiss in Daecheon, crossing the line from friendship to lovers.
Act III: The Rupture and The Ring (Episodes 11–14): Seol-hee catches Joo-man exiting Ye-jin's apartment after an overnight misunderstanding and definitively breaks up with him to reclaim her dignity. She starts an artisanal plum wine business. In the ring, Dong-man faces Kim Tak-soo, who uses an illegal headbutt that causes Dong-man temporary deafness and severe head trauma, leaving Ae-ra devastated.
Act IV: Resolution and Finale (Episodes 15–16): Facing the risk of permanent deafness, Ae-ra demands Dong-man retire. When he refuses to give up fighting, they break up. Meanwhile, landlady Hwang Bok-hee is revealed as Ae-ra's biological mother, who gave her up to shield her from industry scandal while watching over her from afar. In the finale rematch, Dong-man cleanly knocks out Tak-soo with a spinning kick and proposes to Ae-ra inside the ring. Seol-hee forgives a penitent Joo-man after establishing her successful business, and the Fantastic Four celebrate their hard-won happiness on the Namil Bar rooftop.