Under the Blue Moonlight

Under the Blue Moonlight summary:

Haram and Hanul are brother and sister with nobody to rely on but each other. They are also Yin, beings who blur the lines of gender and are shunned by society despite being the only ones capable of giving birth to the blessed Yang. One day, Hanul leaves with a promise to come back soon. But as six months pass without a word, Haram sets out to find him, with the unexpected help of a Yang named Chong Yun..