Shadow Spirits

When the spirit of a Youkai with no wishes that've been fulfilled or who haven't finished their business on a planet dies, on the very rare occasion, these spirits have twisted to become an immortal spirit that becomes charged with the new task of finding a host and helping them achieve their dreams in exchange for a vessel attached to the physical realm. While they initially do sound like guardians, Shadow Spirits can be tricky little beings, especially when they don't care for their vessel (be it through sheer dislike or apathy), the welfare of others around them or are imbued with a bitter energy. Only Youkai who have the element/subelement of Shadow Magic may become Shadow Spirits, as the unique property the element gives their spirits renders them into undead beings.

When the Shadow Spirits have a vessel, they can assume 1 of 3 forms. That of a literal spirit/poltergeist that can choose to be seen by others around them, a shadowy form that assumes the traits of their inner animal (that tends to be their default form), or a more physical form where they're more free to do as they like on their own (though these forms can only be obtained when their hosts are strong enough to support such a thing, and the chains binding them and their host together tends to prevent them from outright running away from them). While symbiotic beings at best, they can be quite harmful when they want to be. As they're extremely rare to come across, little is known from them aside from the fact that they've often got goals in mind to fulfill.

Oddly enough, as of current, Shadow Spirits have only been born from a select family of Youkai, the six of whom died at differing ages but all knew one another in the lives they had before death. Because of their numbers, it's rumoured that having all six of them together in one room is enough to create miracles (which, when they are together, they produce Life Magic, so it may not be too far off from the truth). Rumour has it that if a seventh Shadow Spirit was ever born and brought together with the other six, something special may happen...

Appearance

Shadow Spirits take on one of three forms. The form of a spirit (which resembles their humanoid forms) and can only be seen by those they choose to let see them, that of a shadow-like animal, and a humanoid physical form that may or may not resemble the way they looked in their original lives.

As of current, the appearances of the existing Shadow Spirit siblings are as follows:

Swift - Wyvern

Sacri - Phoenix

Stealth - Kitsune

Strength - Seal

Sorrise - Horse

Siesta - Chameleon

Behaviour

Shadow Spirits tend to only trust their hosts (and on the rarer occasion, the friends and families of the host as well), otherwise tending to stick themselves and do as they like alone. They don't trust each other very much either, despite all of them being siblings (for the time being, anyway), and take quite a lot of time and effort in order to build their trust and earn their friendships. However, once it's earned, they're very steadfast companions who'll always strive to protect the ones they care about. It's certainly worth befriending one if it's possible to.

Climate

Depending on their secondary elements and the build of their bodies, Shadow Spirits can feasibly live anywhere their hosts can live at too.

Reproduction

As the species came into existence when the former Youkai with unfulfilled wishes/desires died and warped into what they are now, it's likely that that is the only way their species will grow at all. While capable of mating, for very obvious reasons, none of the Shadow Spirits have tried to experiment with this. Shadow Spirits also are one of the few species who cannot repopulate through the Magic Seed method, as their energy is too much for a Seed to handle without mutating and/or dying immediately.