Disciples

1.) Mahana cannot force you to do anything
You will absolutely be obligated to do certain things. Defending the Cat's realm from invasions is one such task that you will be forced to do, regardless of whatever else you're engaged in at the time. You could be just about to claim an ancient artifact from an Elaudian temple and the next thing you know you'd be standing in the center of a battleground, minions battling it out all around you. No roll, no nothing.

However, invasions are not the only thing you'll be obligated to take care of. The cat can call you to his presence on a whim. Drag you into his realm against your will. Because disciples carry a piece of a spirit within themselves, spirits are able to work through their disciples. This is most often used when a spirit seeks to create a servant or another disciple, or perform some miracle for its followers, but this control also extends to bringing mortals into their realm. The disciple included.

Generally this is undesirable, because it's taxing to rip someone out of one reality and plop them into your own unless they're hanging out somewhere "close", in so far as realities can be near to one another, to your reality already. Thus, he'd likely on summon Mikhael forcefully if something dire was going on. If a rival spirit's follower was about to launch an Invasion, or if he was being invaded. If he wished to invade somewhere, he'd reach out to Mikhael and ask him to join him in his realm, rather than just ripping him up and plopping him down in front of him. The flip side is that Mikhael would be able to enter the cat's realm through shrines and use these shrines to rapidly travel between places where he's placed other shrines, or anywhere within the cat's fief.

The cat can also prevent Mikhael from leaving his realm once Mikhael has already entered, and within the cat's realm the cat can exert far more influence over Mikhael than he would usually be able to. For instance, say the cat wanted to make Mikhael kill some random mook which Mikhael has never met. If Mikhael were in the depths of Elaudia far from the cat's influence the DC would be 15 to resist. If he were in the cat's realm it would be a DC 30.

2.) The disciple relationship is a partnership.
Absolutely not. Becoming a disciple is always and will always entail that you serve your patron spirit. As I said, when a spirit creates a Disciple it's using soft power to control a mortal. When a Disciple creates a Servant it's using hard power.

The spirit gets a Servant to do what it wants by forcing the Servant to do what it wants through sheer will. By directly controlling its movements, actions, speech, et cetera. A servant gets a Disciple to do what it wants by making it in the best interest of the Disciple to do what it wants. However, in both cases the Spirit still exercises power over a follower.

For instance. Say a spirit wants to launch an invasion of a rival spirits realm. To get a servant to open the portal and launch the invasion he'd take direct hold of the servant and puppet it around, infiltrating the realm of the rival spirit and having the spirit open the portal.

To get a Disciple to launch an invasion of a rival spirit's realm, the spirit would mention that if it could only take this region over here its power would increase greatly, and thus the Disciples power would increase with it. It would subtly point out that this region over here is a great recruiting ground because it happens to contain a large city and its hinterlands which the Disciple could then travel to and from rapidly. It would say that if it just controlled a certain fief it would have the power to create a powerful artifact. Et cetera, et cetera. If it asked directly it would be a request, not a command, but a request that the disciple would be very likely to accept.

3.) The cat spirit will be able to kill Mikhael on a whim, or turn Mikhael into a servant after the fact.
Becoming a disciple is a permanent arrangement. Neither Mikhael nor the Cat would be able to back out of it. Spirits are incapable of harming either themselves or their minions, and since Mikhael would contain a shard of the Cat within himself the cat would be incapable of harming Mikhael. Nor would he be able to take the shard back, because once the shard is incorporated into Mikhael's soul it becomes a permanent fixture, intertwined with the core of his being. When Mikhael dies, that piece of the cat dies with him.

Similarly, the cat would not be able to expand the shard within Mikhael, thus allowing the cat to completely subsume Mikhael's soul, because the soul would reject any further intrusion. Mikhael's soul would in a sense become inoculated to the tampering of spirits. Should any other spirit try to implant its larval young in Mikhael's soul, the larva would be unable to latch. Should any other spirit attempt to implant a piece of itself within Mikhael's soul, the shard of the cat spirit would destroy it's rivals shard. Should the cat try to implant a second shard, or join the existing shard with another to make it larger and more powerful, the soul would harden and the cat spirit would be rebuffed.

4.) Void entities ain't shit with the cat's protection.
I'm making a distinction between Void Entities and Spirits here. Think of them sort of like Matter and Antimatter. When the stuff of a void creature mingles with the stuff of a regular spirit, the weaker of the two is destroyed. Which means in the vast majority of cases the Spirit's stuff is destroyed. You've more or less already been told this IC, when the cat spirit freaked out about Ricky's tentacle, so it's not really a spoiler. However, if I said much more than this I would spoil some shit, so I'll stop talking about it.

5.) Spirit would have you kill friends/family/companions/et cetera
The spirit isn't stupid. Ideally a Disciple should be fond of the spirit it serves. Thus the cat will endeavor to keep Mikhael happy. If one of his companions is actively plotting against the cat, the Cat would ask Mikhael to do whatever he thinks is best to stop the threat to the Cat, and by extension Mikhael's power.

If a spirit did try to force its Disciple to kill a friend/loved one, the DC to resist would be pitiably low. We're talking a DC 10 or so. To the point that you would essentially need to roll a Nat 3 in order to fail.

Thinks that's everything glaring that I saw.