In the world of "One Punch Man," heroes are common and anyone can apply as a hero if they past the Super hero certification exam. Heroes in One Punch Man are the people who pass the exam who then will save everyone from danger. Classification of Heroes are from Class C, B, A, and S, who are the strongest heroes.
Blast is the character that has been mentioned since and shown once in the "One Punch Man" Web Manga comics version. He is the Number one hero in class S, that would make him the greatest and strongest in Hero association. In Chapter 106, this is the chapter where he was first seen, but his face is not clear that's why no one knows yet who he really is.
The scene takes place 18 years ago, where blast save Tatsumaki from a myterious being and this is the reason why Tatsumaki became a hero. This appearance also enbaffled readers as Blast has the same outfit and cape and the same ideology of being a hero as with the main character of "One Punch Man," Saitama.
The outfit of blast in "One Punch Man" has just a little difference on Saitama's outfit, there is like a fiery lines on the zipper. He also consider his job as a hero more like a hobby. Right now Blast is not doing any hero job and the location of his whereabouts is unknown, But Sitch mentioned that when humanity truly needs saving, Blast will definitely come.
This could really mean that Blast is strong. But is he stronger than Saitama? why did they have almost the same hero suit? Why is blast not doing any hero job? We all have a lot of questions about this Character but we will surely know more. We just need to wait for more updates for "One Punch Man."