Possession type

I’m looking for a webtoon where the FL died and became possessed by a forest spirit. He had to eat and devour her body. They are not supposed to to it while the person is alive or they will be stuck in that body. She was eaten alive as requested. People find out she’s not really her but her family protects her as well as her brother and father. She’s very loyal to the prince she serves to protect. She’s a knight.