I must say this is quite a beautiful piece, though I am disturbed by certain details.

Firstly, the snowflakes, to me, appear somewhat large and irrealistic. They look like paper cut-outs and I believe they should be smaller and more transparent. I also do not believe the clouds should be darkened in their middles there, I don't see any light source making so necessary. But as always, your starry night backgrounds are admirable; dreamy.

Now concerning the way you drew your OCs, in this piece comes your recurrent error of drawing animal limbs faultily. I believe the elbow bone does not protrude that much and the wrists appear so thin and bony (Stain).
Tora's expression seems a bit exaggerated, though I love Stain's.
I also love how much the fur shading is detailed but I think it shouldn't be that precise on Stain's side. Tora's tail suffers from this too, but it's more acceptable. I also think that you need to study animal ears more and see how they really fold.
Other than that, I adore Stain's horns but I believe they should leave more streaks or 'taller' streaks than that. Concerning the paw streaks, the only ones I have a problem with are the yellow and red ones; a bit too 'solid', not gentle enough.

But overall, this is a nice piece speaking of calmness, beauty and freedom.