RE: therian vs kin?
Therian means you experience traits that are not normal human traits, or one of much higher level than is normal. It can come with all sorts of 'shifts', or altered states—the common ones being phantom (feeling phantom limbs like ears/tail/wings) and mental (anywhere from small instincts to a totally different mental state).
For therians, these things do NOT go away even if you do not get any exposure to animal-related things—I. E. if you try to live a completely usual human life, they still affect you. And, even more important, you do not have to LIKE these things—you could get shifts aligned with an animal you dislike or felt little outside connection to.
Kin, on the other hand, is self explanatory: it means you feel kinship with something. Kinship, in simplest terms, is belonging—you feel as if something is "your people" or "your kind." You could experience this alongside therianthropy for the same thing, but most of the times it's simple kinship without therianthropy backing it. Kinship can create sensations similar to being therian, but without exposure to said focus of the kinship, it won't be there.
When the light is running low, and the shadows start to grow
And the places that you know seem like fantasy
There's a light inside your soul that's still shining in the cold
With the truth, the promise in our hearts
Don't forget, I'm with you in the dark.