Susanoo is a gigantic, humanoid avatar made of the user’s chakra which surrounds them and fights on their behalf, that has been handed down throughout all the generations of the Uchiha Clan. It is the strongest ability available to those who have awakened the Mangekyō Sharingan in both eyes.
When activated, Susanoo forms around the user and becomes an extension of their will, acting and attacking on their behalf. By default, Susanoo is anchored to its user and they to it: in its less developed forms it will move around with the user; in its more completed forms the user will be suspended within Susanoo, being brought with it as it moves around. This connection allows Susanoo to shield against physical attacks, one that becomes more difficult to penetrate as it is manifested more fully.