Ha! I just read your signature. Irony, considering what this RP is about.
Anyway. The idea that I had back in my first PJ RP was a son of Tartarus capable of manipulating monster dust, which his body was essentially made of. He could make weapons out of himself and even create small-scale monsters, like a hellhound or a Dracanae. Of course, this got shot down pretty quickly by the GM.
As for demititans, it seems more doable, and a bit more grounded than a demiprimordial. If the above is too much, than it will probably be easier. As for which titan, though... I've got nothing.