Hisui no Yumemiru Yoizuki no Karasu

The kingdom of Feng had been at odds with the neighboring state of Kun for many years until they finally signed a peace agreement. However, when the king of Feng senses suspicious activity within his kingdom that might be related to Kun, he orders his trusted court official, Lin Yu, to uncover the conspiracy. Lin Yu assigns the task to his most skilled spy, the cunning Wu Yao. When Lin Yu asks Wu Yao what he wants in return for this dangerous mission, Wu Yao unexpectedly replies, "I want to sleep with you." In Wu Yao's yearning expression, Lin Yu glimpses the face of his long-lost step-brother—the one he's searched for all these years. What fate awaits these two, torn apart by the past and separated by their status and station?

(Source: Gentosha, translated)

Note: The chapter count includes one extra.