Derflinger

Saito's talking sword. Seems to have the power to warp people, as seen in the beginning of the third ZNT series: Princesses no Rondo.

Zero no Tsukaima F spoiler:
He shatters after taking a powerful breath of fire from the Ancient Dragon in episode 10 of Zero no Tsukaima F

On the episode 12 it's revealed that he's not the "sword", he's a spirit that lives within Gandalfr