Who would win 

Risotto Nero JOJO Bizarre Adventures

Or

Saitama from One Punch Man 

My Opinion: this could go ether way and Saitama may have been able to destroy a katana with his teeth that does not mean he's immune to his insides being in pain infact if risottos from a far distance and is invisible saitama won't see him and will die do to blood loss and,how Saitama will die eventually and the way saitama will win is to knock risotto out and just because saitama has the ability to kill people in one punch in his universe does not mean it will actually work on risotto if he can't see him cause saitama needs to see his opponent stil; so he can kill them or,knock them out if their human risotto would win when killing saitama after turning all of his blood into iron and,saitama wins if he knocks risotto out with just a punch