Spirits are extremely powerful beings and are not to be messed with, they can never die except by a spirit blade and when that happens they are either reincarnated or recycled. Spirits are represented by they're god that is controlling them, (god of war controls a spirit of war) and are experts in their titles, having all of the powers of such a thing. Spirits are in each mortal as a power source, in fact spirits are any organics way of power storage, and if you were to activate said spirit it's powers run over you and you have them as well, minus of course being immortal. Spirits when by themselves and in the physical world can take over either dead bodies or live ones, depending on how cruel said spirit is, when a spirit takes over a body it heals it to perfect health and controls it entirely. With said body it has the power to turn to spirit mode and heal all the damage to a body and also go through walls and the like.