Akatoki no Yami

From Baka-Updates: It is the Heian era (794-1185); Kamo Yorimichi is a young onmyouji, the son of a famous onmyouji leader of the imperial court. As a boy, he had been hailed for his incredible talent - but a certain incident during childhood stripped him of all his memories and the ability to 'see'. Koretaka Shinnou, once the crown prince renowned for his brilliant mind and steadfast personality, is now in exile - supposedly as punishment for murder. Upon their first meeting, Yorimichi's powers are instantly re-awakened. Intrigued by what he believes to be Koretaka's amazing abilities, Yorimichi decides to swear allegiance to the prince.