Shizuo Heiwajima from Durarara!!
His superhuman strength comes from pure rage rather than any supernatural source. When angered, Shizuo rips street signs from concrete and hurls vending machines with ease. His body automatically removes the natural limiters that prevent humans from using their full strength. The lack of any magical explanation makes his ability all the more unsettling. He’s technically just a very angry human. His bartender outfit remains pristine despite his violent outbursts, adding another layer of visual incongruity to his character.