When sealed Kage takes the form of an oversized katana with a black hilt and no guard. It is released with the command "Engulf them in Darkness". When released Kage disappears as some form of black energy. This 'energy' can be summoned at will (in limited quantities) to act as a shield, be fired off in small blasts or to increase the strength of the wielders attacks. The amount of energy that can be manifested is limited to approximately a sphere of 30cm in diameter (although it can have different shapes) so it requires great skill to use effectively. When used to amplify attacks and defend, Kage's power depends on the objects it is protecting/amplifying. The stronger the object, the more powerful the bonus Kage will grant (e.g. Kage will grant a larger bonus when amplifying a blade than a fist).
Kage also has the passive ability to be able to completely conceal people's Reiatsu (unless it is too large in which case Kage only partially conceals the Reiatsu in question) even when sealed. This ability can be trained to conceal larger Reiatsu's and the upper limit of it's power is as of yet unknown.
To be added at a later date.