Well according to mythology, Kitsune can technically shapeshift, so they wouldn't necessarily have to look like a fox the whole round.
You could have them take on a human form in order to perform the majority of their actions (opposable thumbs help!), but retain the option to turn into a fox form as a utility of some kind. Perhaps the danger of using this fox form is that the more hearts you consume, the more tails you have, so you'll stand out when people are starting to hunt you down.
I think the servants idea is detrimental to this; we have too many "thrall"-types as is and people generally dislike them quite a lot. Perhaps limit the servant to one person, considering the myths around Kitsune tricking men and women into marrying them, but it acts like a mindslave implant. That way you have to make a very important choice as to who you "befriend" and when, and it encourages the resumption of roleplay if you want your servant to remain inconspicuous. If your servant dies? That's it, no more servants. Protect your tools.
Granted, this idea comes with its own risks, as there are a few players and antag mains who have a large friend pool to choose from, so you'd end up with people willingly being enslaved. You'd also have the problem of people using the servant to murderbone the station, or the kitsune immediately bumrushing someone of high status to enslave. These issues would have to be ironed out and considered if this develops further than a concept.
Make eating hearts the ability and goal from the get-go, with the rewards coming at 3 (small), 6 (moderate) and 9. 9 turns your objective into pure survival; get on a pod or the shuttle and book it out of there, ready to do it all over again to some other hapless group.
I encourage creative thinking and the utilisation of foreign mythology to make interesting antags for this community; keep thinking and working on it!