The main reason why Van Lucy can't be said to be a mechanic doll from the underworld is because the blood of a god runs through its veins. Rather than being just a mechanical device, the structure it uses to move its body is closer to that of a living being. It resembles a god with muscles made from metal. There is also the possibility that it is just a god with an awkward appearance, and thus the Summoner's Council is conducting further research with the hopes of reproducing its godly powers.
A mysterious liquid that leaked out from the head of Van Lucy.