When the time came for One Punch Man to be adapted for animation, the job fell to Madhouse, the studio responsible for producing classic anime titles like Ninja Scroll, Death Note, and even Cardcaptor Sakura. Needless to say, that track record brought some high expectations, but with OPM, they managed to blow everyone away with how beautifully they handled the fight scenes.
It's a tough job, too. Murata has an incredible ability to capture movement in still images, picking out a single moment that captures an entire fight scene in one gloriously violent panel, and since he was working with ONE's pretty perfect comedic timing, it was difficult for fans to imagine what animation could add to it. When we actually saw the fight scenes that they were making, like their adaptation of Saitama's "sparring match" with Genos in the Manga's 17th chapter, it was pretty clear they could add a whole lot.
The secret? It's all in the frames. In an installment of the web series Amazing Animation Analysis, animator Florian Walraven goes frame-by-frame through the fight scenes of the first episode to explain how Madhouse made Saitama's single punches look so believably devastating, and a lot of it has to do with how they staggered the characters' movements. Rather than have them acting in the same cycles, their movements in the fight scenes are offset by one or two frames, giving the sense that these are people moving independently of each other, and reacting in real time to the other's attacks. The result is some of the best fighting we've seen in anime in a long, long time.