It's about a Korean girl w cancer and transported in a book she was reading. In the book, she's a princess that was born from the queen and she was part of the kids that vie for the throne. Father is neglectful to kids but loves his wifey very much. In the sword choosing ceremony, MC chooses her dad instead of swords. She's also time limited, since she dies at the age of 21, and the main antagonist became her tutor.
It's about a girl that can cure diseases with her blood, a noble that took care of her and used her blood and shit to rise in power, and then another guy with supernatural powers help her leave her shitty life. Supernatural dude is also murderous asf and apparently has an untold past with our girl.
Pretty sure it’s this one: https://www.mangago.zone/read-manga/heeran_love_song/
LEAVE THEON AND GO AFTER YOUR MANS BEFORE SHE SNATCHES HIM AWAY THE FUCK