What can Muggles do?

[awa]

Saitama, if put in our world or GitS world, would have no reason to ever crack mountaints or alter shape of the moon. All of his impressive feats of destruction exists in reaction to other superpowered folks.

He'd be the guy who occasionally stops a cybernetically augmented robber etc., but everyone would dismiss it as a fluke since he has no training or history that'd justify suspecting he's anything special. His training regimen is a joke and nothing noteworthy even in his own setting. In GitS, anyone would be able to tell that Saitama's fitness routine could not explain his powers & trying to repeat it wouldn't work.

its true his training regime is a joke, but the first time he punts a runaway tank into orbit the government if not the world would notice. They aren't dumb enough to see that and think its just a coincidence (like they do in his own world) and that assumes a best case scenario of the character keeping to his original roots and not trying to actually do anything with his power. A non joke character would probably want to do something with their godlike power which would cause the world to take note and then bends the setting around him.

sit ups might not be able to replicate his strength but you can be sure they would try and figure out his secret even within his own setting a few people do that.