The concept of the story is quite interesting, too bad it is only a one-shot, I wouldn't mind reading more about Futagami. At one point it was actually pretty freaky, and gave me the chills (it just had to touch on something I really hate and am afraid of), although the first half of the chapter had a lot of information to absorb.
It would be really nice if we could find out more about that world, still a lot of questions and so much potential. The story is quite good, but the art, the characters look so similar to some other characters in other manga, although that could just be the art style of the artist.
The ending event was great, although it is one of the more typical tricks where the protagonist manages to tap into a large amount of hidden power that he never knew he had it in himself.
Surprisingly enjoyable, its fun to read, interesting, and exciting, definitely recommend this one-shot manga.