So I have been into this anime recently called attack on titan and I love it! it has the right kind of horror, mystery and adventure that someone like me wants! But here's the thing, how is it that the titans even exists? we all know that this world that attack on titan is set in doesn't revolve around magic and it's obvious that their technology is far from being able to find the thing we call DNA to manipulate it, however, since this is to be taken in the future and humanity is in a 'three-layer concrete cage' I have been really wondering of what the titans are and how they are made. (slight spoiler) than it was revealed that they are humans.   So here is my theory in story form.
p.s. (r.f: Aot-style) means Rainbow factory: Attack in titan-style.