Hydra

Hydra was the unnamed Quirk possessed by Nine, who stole it from an unknown hero.

Description
Hydra allows Nine to summon a gigantic sea snake or dragon-like creatures from his back that he can control at will. The creatures are large enough to crush a person in their jaws. Nine usually summons one or two of them at a time. It is unknown if this is really the definitive reason why this happens, but when Nine is enhanced by a drug he becomes able to summon a plethora of these creatures at a time.

Nine generally reserves this power to surprise enemies who attack him from behind or dodge his Air Wall.