This is a tricky one! The creatures are, strictly speaking, reflections of characters' experiences and expectations, so game lore-wise there's no trouble. Meaning specifically, these would not be "real" titans, more like facsimiles of them, so no soul required.

We do think this would be a particularly rare creature, though, so maybe not one to have in repeat settings. But overall we're open to the idea if you think it would be interesting to play with!