Psionic powers, like everything else in the game, are defined by a Aspects, Skills and Stunts
Every psionic character must have at least one aspect relating directly to their powers. It is possible to create a character with a very low-powered minor talent with just an Aspect. Such a character won’t be able to do anything a “mundane” can’t do, but will still be able to get bonuses to skills for the cost of a FATE point.
Unlocking Psionic Skills
Most psionics will have one or more psionic Skills. Since these skills grant abilities above and beyond those of non-psionic characters, a character needs a special stunt to “unlock” their powers.
For the cost of one Stunt, a character may have a single psionic skill, at a level no higher than Fair. At this level you’re still a minor talent, relying largely on your more mundane abilities.
For the cost of two Stunts, a character may have up to three psionic skills. All must be thematically linked to a single aspect, and may be any level up to Good. At this point you’ve got a bit more power and versatility, although your more common skills are still going to be more important – your best skills won’t be psionic ones.
For a cost of three Stunts, a character may have up to six psionic skills with a maximum level of Great. The skills may either all be linked thematically to one Aspect, or may linked to two different aspects. At this level, psionics is your main ‘thing’ even if it doesn’t totally eclipse your other skills.
For a cost of four Stunts, a character may have up to ten psionic skills, with a maximum level of Superb, You must have at least two psionic aspects, and each of your psionic skills must be thematically linked to one of them, At this level your best skills will be your psionic ones.
On top of the stunts required to unlock powers, you can build additional stunts off a psionic skill in exactly the same way as any mundane stunt; such as substitution of a psionic skill for a mundane one, or +2 bonus for a specific usage of the skill. More potent psionic abilities over and above the listed psionic skills require further stunts. Depending on how potent the ability is, such a stunt might cost equivalent of two or three simple stunts, or may require a FATE point to activate.
One thing that will require a stunt is any use of a psionic skill for any kind of attack intended to cause death or physical injury.