Blast is the #1 hero of the Hero's association, but we have no idea who or even what Blast is with the hero never making an appearance.
It also doesn't seem like any of the other S-Class heros have seen Blast.
I'm curious if anyone has any thoughts or theories on Blast's identity?
My pet theory is that Blast is actually a position made for Saitama by the the founder of the Hero association
(the wealthy grandfather of that cleft chin kid Saitama saved starting his career as a hero).
Not knowing who saved his grandkid, he reserved the #1 position under the name Blast for Saitama if he ever came forward as his grandson's savior.
It also works to encourage the other higher ranked hero's to keep accomplishing heroic deed in order to compete with the mysterious Blast.
I imagine the mangaka One would reveal this through another character like Genos finding out that the position was reserved for the grandson's savior, though without actually knowing that Saitama was the one who did it.
I doubt Saitama would actually accept the position even if it did come out, which kinda makes the series all the better.
Of course, Blast may actually turn out to actually be a character, but it's an interesting idea to consider and I'd like to hear if anyone else has other theories or information on Blast's identity.