Kitsune no Yosuga
Kokonoe is the last fox in the forest, and one day while patrolling his territory, he happens upon a young bird who fell out of his nest. While Kokonoe initially picks up the bird to eat later as "emergency rations," he eventually can't let go of the child and decides to raise him as his father, giving the child the name Yosuga. But when Yosuga the hawk grows up, he and Kokonoe both start to yearn for a deeper connection between them, despite the barriers of species and gender, and Kokonoe feels he's stealing from Yosuga what it means to be a hawk, so he must let him go. If you're squeamish about incest themes, do not read. Otherwise, I think it's a fairly touching and interesting story with beautiful art. Trigger warning: incest themes (adopted parent x child)
Oyasumi, Itoshiki Kotori-sama