Soleil

-Was born prematurely, and wasn't expected to live long. Against the odds, she's somehow survived til adulthood.
-Has a body so weak that her own magic power is slowly destroying her physical body. Like it's literally breaking down, and only the power of a ton of money is keeping her hanging on. Can't actually use the magic flowing through her veins, though someone absorbs the excess magic everyday.
-Gets ill easily, and it's really a miracle that she's survived so long. Due to her condition, she can't overstress herself or get angry because it could actually kill her.
-Looks much younger than she actually is. Short and sickly pale.
-Has a lot of theoretical knowledge, but due to her condition doesn't have a lot of...practical knowledge.
-Lives vicariously through her writing, though her main character is very clearly a self-insert Mary Sue and the circumstances in her story are quite unrealistic. She can't really be blamed for it though, since she's never experienced what having a normal life would be like, and could only guess.
-Youngest Miss of the Komachi family. Has two extremely overprotective parents and three older siblings that'd murder someone for looking at her the wrong way.
-A bit of a miracle in more than just one way. She has the strongest magic power that's been born in awhile, which makes her situation just that much worst since its literally breaking her body down.
-Attempts have been made to cure her but at best they haven't worked, and at worst they've only made her even weaker physically.