Progression of Power

The martial artist focuses her chi through a series of disciplined combat forms. The mecha pilot brings weapon systems online one at a time. In the process, both become more powerful.

In Fate, you can model this with a series of create advantage actions that generate free invokes. While they give the normal benefits of invoking an aspect, free invokes are only good for one use. After that, invoking the aspect costs a fate point as normal. Some players dislike the idea that an advantage is only beneficial when you can pay for it.

Instead, consider the following stunt skeleton:

You get +1 to [skill] [in a situation appropriate to a normal stunt]. You can spend a free invoke of an appropriate aspect to increase this bonus by +1 for the rest of the scene. This bonus cannot exceed the campaign's skill cap.

If you take the time to create appropriate advantages, you can power up way beyond the bonus of a normal stunt. You still get a small benefit even without powering up. This is just a rough idea, but it could be interesting in the right campaign.