Saimin Reiki

A devil appears in front of the main character, Nil, who lives as a guy.
“You are the blood of the royal family who was abandoned as an abomination,”
said the devil
. “
Why don’t you take revenge with my’power to manipulate humans at will’?”

Nil, who gained power through a contract with the devil, slaughtered his twin brother and replaced him as the crown prince.
Further hatred was directed at her mother, the Queen, and her sister, the Princess.
What is the end of a man who has the power to be a human being?