Sanctaphrax, I hope you don't hate me for offering a possibility for how your rebate idea might work. Please don't let it stop you from putting up your original concept, which will probably be better than mine anyway. I just wanted to put it up for review so that everyone could give some constructive feedback on what they think doesn't work, and maybe jog some imaginations in the right direction.
Companions
Companion stunts grant a player character a dedicated ally, a fully formed character in their own right who has a strong motivation for helping the player out. In addition to purchasing the relevant stunts, a player must choose an aspect on their character sheet that defines the relationship between himself and his companion.
The companion has its own High Concept and two additional aspects, all of which can be compelled by the GM as with any NPC. The player does not gain fate points when his companion is compelled, though he may choose to spend fate points to resist those compels or to invoke the companion's aspects for effect or declarations. The companion may not have or spend fate points itself under any circumstances.
Companions are NPCs and ultimately they are under the control of the GM. But they are assumed to be completely loyal to the player who purchased them, and so barring compels they should obey all reasonable orders or requests.
If controlling a companion becomes burdensome for you as a GM, we encourage you to hand over control of the companion to the player who purchased it. But be aware that in the hands of a clever player this can create a significant increase in power.
Stunts
Trusty Ally: You are accompanied through life's travails by a devoted ally. The relationship between the two of you might be personal, professional, mystical, or anything else, but come hell or high water, you are in it together. Choose one skill thematically appropriate for the type of companion you desire, for example Survival for a pet, Resources for an employee, Lore for a supernatural familiar, Contacts for a devoted old friend, etc. This stunt now applies to that skill.
Your ally has no refresh to spend on powers and stunts, but has a skill pyramid whose apex is one below the level of the skill you used for this stunt.
Partner: (Requires Trusty Ally.) You're not interested in a sidekick so much as a partner, someone who can keep up when the going gets rough. The companion you gained with the Trusty Ally stunt is granted 1 refresh to spend on stunts and powers, as appropriate to their High Concept. You may purchase this stunt again, each time granting your companion 1 more refresh. Unspent refresh does not allow the companion to possess or spend fate points.
This refresh give the companion more scope to interact with the campaign, making them useful in a broader array of situations than an unimproved ally. Your GM has the final say in determining how powerful you can make a partner before it becomes inappropriate for the campaign.
More than Competent: (Requires Trusty Ally.) Good help can be so hard to find – but you seemed to have lucked out. Your companion is broadly competent across a variety of skills, making her an indispensable asset in almost any situation you encounter. Increase the level of your companion's skill pyramid by 1. You may purchase this stunt again, each time increasing the height of the pyramid by 1.
These skills give the companion more scope to interact with the campaign, making them useful in a broader array of situations than an unimproved ally. Your GM has the final say in determining how powerful you can make a companion before it becomes inappropriate for the campaign.
Quirks
Not all companions are made equal. Some are single-mindedly devoted to the player, others are not quite. Some don't see themselves as companions to the player character at all, and might have their own ideas about who is subordinate to whom.
Quirks are ways to refund an amount of refresh spent on companion stunts. You may choose a number of Quirks equal to the number of Companion stunts you have minus one. Each quirk you chose refunds you 1 refresh, in essence canceling out the cost of one companion stunt.
Unreliable: While you can count on most companions to be available whenever you need them, yours is a lot more mercurial. Whether it's because of other commitments, or because they are just plain ornery, a lot of the time they just won't be available to help out. Change one of the companion's aspects to reflect what makes it so unreliable. It should be common enough to come up at least once a session. When the GM compels that aspect, making your companion unavailable, you are not eligible for a fate point.
Out of Control: Some part of your companion's nature makes them difficult to control in exactly the situations that you most need their help. Change one of the companion's aspects to reflect what makes it so uncontrollable. For example, an animal may respond poorly to commands during stressful situations, or an overbearing, overprotective father may “know what's best”. In most situations your companion tends to follow your wishes. In really important conflicts, however, their nature gets the best of them and they get carried away, introducing further challenges to the player who they are supposedly assisting.
Focused: This ally tends to be useful in one or a small group of related situations, but not in others. For example a secretary ally would be good at doing research and deflecting unwanted social attention, but would be of less use in a fight. Choose a focused role for them and keep it in mind when designing their skills and aspects. Whenever the ally is called upon to aid in a situation outside their expertise, they become timid or unwilling. At best they manage to stay out of trouble in such cases, at worst they become distractions or, through their inexperience, make things worse.
Companions, Compels, and Quirks: A basic companion should be available to the player who purchased it more or less all the time. While the GM does have control of it and may compel it's aspects at will, those compels should have more to do with guiding the companion's behavior within a scene than preventing them from being useful. The player did spend the refresh, after all, and should be able to benefit as consistently as they do from any other purchase.
There will be situations where it just doesn't make sense for a companion to contribute, or even to be present. If something prevents a companion from contributing at all to a scene, it is likely worth a compel against the aspect the player took defining his relationship with his companion, and thus a fate point. Keep in mind the guidelines for weak compels (YS 104) when making this decision.
If a companion is unavailable or unwilling because of a Quirk, it is never worth a fate point.
Credit where credit is due: This set of stunts is a result of many minds coming together, and is not my own invention. Special thanks to Sanctaphrax, whose ideas I used for the quirk system, and whose writing I quote from verbatim here and there. It is also by no means meant to be a final system, so please rip it to shreds and lets build something that does work.