Your character were killed once by the royal family for the things that he did not do. Both the King and Queen agree to decapitate him in front of all the peoples but not the princess (my character).
The princess tried to stop the King and Queen but she was too powerless and had to remain silent. All she could do is watch the event till it ended. She prayed that someday she could leave the castle.
Later he was reincarnated but now he isn't the same gentle person as he used to be anymore. He wanted to destroy the royalty so he decide to use his demonic power which he was granted after his reincarnation to sneak in the castle. The princess later raped and kidnapped by him with a reason to make both the King and Queen panic before he make his move to kill them.
Male Lead will be sadist character.
Male lead has a feeling towards the princess but he had to destroy her first for his revenge. He wanted to use her as one of the tool for his revenge.
Princess may or not be torture before the male lead took her in. This is both RP-ers decision to make.
Later story will have the male lead to slowly fell in love (again) with the princess as she never leave his side. He will also find out that she never agree with her parents for killing him. He will still use her for his revenge and sexual desire.