Demon blood was awarded only to the winners of the clan war (whatever it's called), and only exists in like 8 "copies" what so ever. Veb's Demon set was not too long ago sold for $200, and that's dollars, not credits.
I guess you saw it in the shop for 1 credit, and, well, who can blame you, how could you know?
Anyways, now you know, you're not gonna get Demon blood any time soon.