This new trailer for the game sheds a little more light on how things will actually function. As it turns out, yes, you will be able to knock your opponent out in one hit -- but there's a catch. You start battles as a different character, and the better that you fight, the faster Saitama arrives on the scene. Once he gets there, you basically can't lose.
We assume this mechanic is a story mode feature, but if that's the case, does that mean Saitama isn't playable anywhere else? Surely not? It's a fun mechanic, but we still don't really understand how it'll be balanced. If he's allowed online, we know who we're maining!