Parasite is an Element that Blaid took for his own when he joined Organization XIII. Though not one of the most powerful Elements, in and of itself, it had the potential to make the user powerful.
It can assimilate and absorb the elements and energy of whatever it touches, giving Blaid a large supply of elemental energy that he keeps stored away. From the destuction of the Organization, it is assumed that Blaid can even absorb people. Estimates say that an Artifical Kingdom Hearts is also a possible target, however as of yet it is unproven. Blaid didn't abandon using the element after the downfall of the Organization.