Make it a world skill line: Taming.
Either have it be nothing but passives that you invest in so you can tame better pets. Start with fox and dogs, upgrade to coyotes and forest cats, then ultimately to lions, bears, crocodiles, wolves, etc. Then other passives that increase the power or usefulness of said pets.
Maybe put in some actives that give the beasts abilities, but make one active be the "tame" ability where you need a reagent of some kind for each pet you'd like to tame.
I think it would be pretty nifty.