Help, lost manga.

Anyone know the name of a shoujo/josei manga where the main character was a big sister whose sister had recently died due to illness. The little sister was previously arranged to marry a son from a prestigious family and after she died, the son suggested he marries the older sister instead. Nobody but him is really sold on that idea, and the older sister especially feels guilty about the whole situation.

I remember the art being kinda unique, with very simplistic style and bold, clean lineart.