Sorry for the late reply but I’ll pretty much summarize the beginning so you get the gist of the story without revealing the main surprises.
Mc was neglected child as she grew up with only her mother and sick sister. Their father didn’t pay much attention to them since they weren’t born with blue eyes which showed their royal blood. Hence why they struggled in poverty despite being princesses. The mc discovers that they have an illness which according to records, has no cure. She decides that she didn’t want to live working for a family who didn’t care with the little time she had left and goes to meet her favorite character. Mc didn’t expect anything from them and simply wanted to live the rest of her days admiring the character that brought her comfort in her previous life. She proposes that she lives with him only for two months(the time she was told she had left) and he was going to reject her but thought she could be a good wife since many other women pursuit him. Mc didn’t expect it at all but agreed anyways. Then it goes on from there.

summary anyone