Hi!
I read this a while ago and can't remember the name...

I think it had yaoi undertones, but was about a demon that was being kept prisoner under a demon castle(?), I remember he was half submerged, and possibly the illegitimate son of the demon king (?).
I think he was tormented by his half brother/ brother has sex with him, but that was back story...
He escapes and a healer/doctor picks him up, the prisoner tries to repay him with his body (again very subtle) but the healer refuses...

Also the king or the most powerful legitimate prince keeps a pair or demon brothers as Grim reapers, but they will be killed if they dont obey him. I remember the older one tries to protect the younger one, but the younger one tries to help and has to kill some demon monsters in an underground cave? Also the younger one has split personality (?) and sleeps with the older brother when he is his other self

It was quite a dark story but i remember the art was beautiful... can anyone help?!? Sorry I can't remember more... 🙁