Monster Factor:

The Monster Factor, also known as the Chaos Factor, is the main reason why monsters exist on Terra Sol.

What is the Monster Factor:

The Monster Factor causes a mutation in the specimens aether signature to something more deviant. A creature with such a deviant aether signature is what is referred to as a monster.

Difference between those with and without the Monster Factor:

A creature with the Monster Factor will grow more monstrous characteristics, either physically and/or mentally.

An example of the physical changes is that of a regular rabbit and the Horned Rabbit, which has, as everyone could guess, a sharp horn it uses to defeat enemies. A creature with the Monster Factors turns more battle-ready, gaining powers related to fighting and/or surviving.

The mental changes include more aggressive behavior as if trying to find a reason to use their greater-than-average powers. Other changes include more ruthless and bloodthirsty behavior, mostly found in the lower-ranked humanoid-related monster species, which makes them too homicidal to be considered part of mankind. Fiend Goblins is a good example of this.

Another important point is that the Monster Factor allows the owner to evolve easier, either by a lower level cap or through eased evolution requirements.

How to obtain the Monster Factor:

A living being can obtain the Monster Factor in three different ways:

The first method is by being born with it, while the second method is to evolve into a species with the Monster Factor. Note that one cannot evolve into a species that lacks the Monster Factor once you have obtained it.

And the third method is through being forcefully granted it. This often leads to a forced evolution. An example of this is being forced to turn into a vampire by monstrous vampire-species.

Objects gaining the Monster Factor:

Some objects can obtain the Monster Factor due to lengthened exposure of raw aether, granting them life as monsters. This holds even for untouchable objects like shadows, fire, and even aether itself.

Evolutions affected by the Monster Factor:

The Monster Factor will lock the owner to only being able to evolve into other monster species. Some cases can make different species evolve into the same monster variant. Both a cattle Beastkin and a cattle Therianthrope can evolve into the monster species, the Minotaurus.

Demons and Celestials:

All demons have the Monster Factor from birth. Even those that are classified as humanoids. This is also the reason why demons have the widest selection of species.

This special Monster Factor is also the source of their [Demon] title, which has lead people to call it the Demon Factor. When a demon gains enough power, the Demon Factor will develop to the next stage, granting the demon the [Arch-Demon] title. This Factor can also be cultivated, which has resulted in the creation of the demonic nobility.

The Celestials have a similar case, but their Celestial Factor acts like an Anti Monster Factor, making it impossible for the Celestials to evolve into monsters, except for the few cases of monstrous Celestials. 

It is also possible for these two Factors to merge together.

The Demon Factor can turn into a Tenma Factor, which means that a demon has ascended to the point of being equal to a Celestial.

On the other hand, the Celestial Factor can turn into a Fallen Factor if the Celestial is exposed to demonic aether for too long.

Chimeras:

A Chimera is only possible to be created through creatures that all have a Monster Factor. The Factor acts as a linchpin to prevent the Chimera from experiencing any rejection symptoms. This also holds true for creatures that gain new body parts at a later date, due to their nature, or their skills.

Marc's comment: I was wondering why Lily only wanted monsters.

Garami's comment: Does the Factor taste good?