Kitsune Bloodline

Your blood is so fey it is noticeable and disturbing even to other kitsune. The sorcerous powers within you are based on the kitsune's affinity for illusion and foxfire. Both of these racial traits are augmented through your arcane fey blood. More then likely one or both of your parents had the capability to become a nine-tails.

Greater Foxfire- Greater Illusion Sensitivity

At 1st level your racial foxfire(Produce Flame) cantrip is enhanced and replaced with the Greater Foxfire cantrip. The cantrip doesn't count against your number of cantrips known. This spell is now so instinctual to you it overrides any other form of fire damage you would cast. You cannot cast any other fire damage spells. If a spell uses multiple damage types including fire you may cast the spell fully with the non-fire damage type.

Illusion is part of the kitsune's fey nature. When a kitsune sorcerer encounters an illusion they have not seen before they can easily see through it and usually reproduce it at a later time. You gain illusion spells at the sorcerer levels listed. 

Illusion Spells
Sorcerer Level
1st- Minor Illusion, Silent Image, Greater Foxfire
3rd- Invisibility, Mirror Image
5th- Phantom Steed, Major Image
7th- Greater Invisibility, Hallucinatory Terrain
9th- Mislead, Seeming

Enhanced Tail Casting

Kitsune sorcerers can cast some spells completely with their tails instead of using verbal chanting.
At 6th level, all illusion spells you cast are automatically under the subtle spell metamagic enhancement as these spells are cast by your tails.
If your tails are not free you can't take advantage of this feature.

Foxfire Cloak

At 14th level, you learn the Foxfire Cloak spell. After years of training with your flame you have now advanced your technique enough to wrap yourself in your blue fey flame. This does not use your known spell count.

The Nine-Tails

A nine-tailed kitsune is extremely rare, powerful and considered a true immortal fey creature. The kitsune is conscious when they gain their last tail. The foxfire and illusions created by this event cover a much larger area, last a week and can even open temporary portals to the Feywilds.
Once a kitsune becomes a nine-tails they rarely stay on the Material Plane. Most will retreat to the Feywilds to live a solitary life.
The oldest nine-tails are on par with the Archfey. (Note: most kitsune warlock patrons are usually a blood relative.)
Their ties to their clan usually recede and they only honor ties to blood at this point, though there are exceptions (usually shrine maidens and shinto priests).
They are still humanoid but can transform into a huge nine-tailed fey fox at will and retain their senses and magic casting ability.
Their illusions become semi-permanent true illusions and their foxfire can rival that of the oldest dragons.
Their truesight is absolute. They can detect, see through and dispel any illusion magic.