LF Isekai Manhwa

I'll try to give information based on my memory :P

FL (protag): Girl from Korea. Has short brown/blackish hair? She was reincarnated into another world as a female character with long silver/white hair and blue eyes. The FL has a butler who she likes and was her favorite character from her past life. She cried when he died trying to protect the original holder's body.

ML: Butler with black hair and red eyes. I think he's the mage of a tower, or something. He is in love with the FL's original host and was taken in by her at a young age. I remember a scene where OG FL said his magic looks like "fireflies," or something. He finds out later that FL's soul has taken over OG FL's body, but falls in love.

OG FL (antagonist): Her body was given to FL. Switched bodies (souls?) to be with a prince she loved. The prince killed her family (?) but she was still in love with him for whatever reason. She was a skilled swordsman.