A Brief Explanation on Fae: (Some Spoilers)

How the Fae work is as follows:
Fae are each granted power and a title by the King of the Fae, or one of the Fae Lords. Those granted by higher nobility, such as the King himself tend to be more powerful.

When a Fae bonds with a Magical Girl their Magical Transformation Chant is born. This chant is far more important and far more complex than most people think. The length of the chant, and how well the chant rhymes is determined in part by how closely the Fae's nature connects to the Nature of the Magical Girl they have chose.

Furthermore, the strength of the Magical Girl's powers are directly linked to how well the chant rhymes and how many lines are in the chant. Erika's chant Rhymes and contains 3 lines. This makes her transformation significantly more powerful than most.

When it comes to Magical Girl Transformation a minimum of 10 Magical Points (aka 10 times the Magical Power of the average human) is required for one to transform. In cases where a Magical Girl is unable to transform, she may still be granted a weapon or a spell to fight with, though the power of said ability would be largely reduced until the Magical Girl was able to maintain her Transformation and fight.

(Spoiler) To those who have read to Act 3 you may have noticed that the new Chants of the various Magical Girls only contain two lines, whole Erika's contains a third. And you may also notice that many of their Chants rhyme but don't Rhyme with their Magical Girl name. These factors are all influenced by the compatibility of each Magical Girl with their respective Fae.