Nokemono Ouji to Bakemono Hime

Shuu, the prince of the human kingdom, is afflicted with an incurable disease and banished beyond the massive castle walls to the land of monsters. In his despair, he is rescued by the beautiful monster princess, Misaki. Shuu finds himself increasingly captivated by her and the fascinating, different culture of the monsters. (Source: Fantasia Bunko, translated)