Help!

I suddenly remembered something I forget to finish but can’t seem to remember the name of.

From what I remember the Mc was a white or light pink haired man who was crippled and he had the job of killing the “Prince” by feeding him poison. The “Prince” had these curses on his body and was blind. Eventually he grows up and starts killing his enemies blah blah blah n the last thing I remember is that he overtook the “castle” and has his like demon shadows guarding it but I don’t think he remembered that the MC tried to kill him. Also he could read minds but could only see the MC saying how he’s “eating good” n positive things so he kept him around.