Fabulam Duo Monibus.

In 3012 the world is much the same as it was a thousand years before except now they experiment on people. Satanism and Science have come together. Using a series of rituals and injections of Demon cells into the blood you can turn a human into a demon. David is a boy whose father used him in such experiments. Demon is the little boy who was also exposed to experimentation but not for long before David's father died. This is the story of how David and Damen live.