You know what wouldn't surprise me: Saitama being Blast.
Think about it either:
1)Blast gets bored with being a hero, and does something that changes his memory to forget about it, as well as the "loss" of his abilites.
2)Blast gets hit with some sort of attack that makes him forget who he was, with the belief being so strong that he litereally becomes a normal person.
Either way, his desire to be a hero caused by that fighting that lobster/crab monster start reigniting his abilities, and all that is left now is for him to remember who he really was.
This is just one possible theory. Of course, it could be that Blast went rogue and is going to be the final "ultimate" boss at the end of the story.