He is on the smaller end as size goes for dragons in my setting, but he makes it up with his excellent maneuverability and speed in the air. Also he's a bit of a shapeshifter; he can mostly just switch between his small and large forms, and change small details like the tail tip.

When they first met, Animus was dying. Tork decided he had to save him, almost died himself, and in the process managed to inadvertently soulbind them together.
Ah, Animus is not his real name. Or rather, it is now, it wasn't before. He's pretty secretive about his past, not even Tork knows much.

Animus is indeed soulbound to Tork, but that relationship is not something either of them really wanted, or sought.
It's mostly the result of Tork's overconfidence and hubris, pushing him to try and save everyone he possibly can (or can't).