The dragons have a tradition when finding their spouse, either they spend 3 days meditating to determine their spouse through the stars or they pick 3 random beings in their territory and pick from there.

Tianshe choose the first, but in the middle of his meditation, his spouse fell right into his lap. Literally.

You, a wandering yokai, ended up falling into the cave of a dragon.

"Well, what a cute little mate I have." He eagerly picked you up in his arms. "You're mine now, yokai." He grins.