For Reasons™, Caleb grows wings. Yasha has Feelings™ about this. Caleb, probably having read about Aasimar and knowing that she's fallen, has at least some understanding of how she's thinking about wings, and tries to explain he doesn't, y'know, deserve wings. In the way that Aasimar deserve wings.

Meanwhile Yasha's taken up grooming his wings because it's important that they're taken care of.

Maybe some mutual self-loathing with a sprinkle of wing-mentorship and a dash of wingsex and a solid side of trying to make each other feel better about their pasts?

Or really anything that involves Caleb, twitching but trying to stay still (for her), as Yasha grooms his wings (for him), both of them determined to take care of the other.