The usual AU, but this time, your quirks have some special changes— they can manifest as their own person. In this case, they can hide their presence from others, only you can see them, or they can let themselves be seen by all. If you will them to, they can even help you out and control you, seeing that they're technically an extension of you, your soul and your quirk. They've got their own feelings, their own thoughts, and everything.

NOTE: Izuku's version of this is having past users of One For All guide him, however discreetly so.