The Prince in the Background

In this story, there is a scorned female lead who goes back in time after being unjustly killed by the people she once loved and a male lead who loves and supports her through her quest for revenge. And there are villains, of course, the people who had abused the female lead, the ones who had neglected the male lead, the targets of her revenge in this second life. And then there was Prince Rian, a somewhat plain, sickly character who had barely shown up only to be immediately dismissed as non-threatening and then dying an unremarkable death in the epilogue. Well, it took me a few minutes to figure this out - but it turns out that the sickly background character that shows up in 2 sentences of a 300 chapter novel - well that's me.