Roro-chan wa Kahogo na Kyodai Musume

(Translated from Amazon description) Paolo, a hunter who makes a living hunting monsters, sets forth into unknown lands to capture a legendary Divine Dragon... but when losing his grip while climbing a deep valley, he loses consciousness. And when he comes to, he finds himself in a bath with a legendary dragon! And she's adorable! Now kept against his will as a giant dragon girl's pet, the initially hostile boy tries to escape, but... when he sees how earnestly this giant girl takes care of her pet (him), his feelings begin to waver. Should he run, or let her keep him? A gentle giant girl and a tiny hero's fluffy, heartwarming... pet-raising comedy!?