For those who are lost, the story so far: well the crowned prince wife gave birth to twins which was considered a bad omen so one must be killed. The ministry could not kill the baby so he (Sui) was raised by monks in the mountains. As a grown up monk Sui met a boy (Douman or Itsui) who had survived a massacre and he raised the boy out of pity since the boy had demon blood in him. When the demon blood awakened Douman attacked Sui both physically and sexually and was discovered by the monks of the temple. The monks wanted to kill Douman and Sui protected him, by offering to become a vessel for his twin brother curses. In the process some of Douman cursed demon blood mixed with Sui's blood so there's a connection between them. Meanwhile Sui sends a monk (also with demon blood in him) to protect and teach Douman. So now Douman is fighting those who raise courses against the prince in order to protect Sui from the pain that is cause by being a vessel.
(warning its a spoiler)...
For those who are lost, the story so far: well the crowned prince wife gave birth to twins which was considered a bad omen so one must be killed. The ministry could not kill the baby so he (Sui) was raised by monks in the mountains. As a grown up monk Sui met a boy (Douman or Itsui) who had survived a massacre and he raised the boy out of pity since the boy had demon blood in him. When the demon blood awakened Douman attacked Sui both physically and sexually and was discovered by the monks of the temple. The monks wanted to kill Douman and Sui protected him, by offering to become a vessel for his twin brother curses. In the process some of Douman cursed demon blood mixed with Sui's blood so there's a connection between them. Meanwhile Sui sends a monk (also with demon blood in him) to protect and teach Douman. So now Douman is fighting those who raise courses against the prince in order to protect Sui from the pain that is cause by being a vessel.