Boukansha no Koi

"I want to be by my sister's side until the very end..."

In the autumn of her twenties, Rachel marries her childhood friend Noah, who had been her longtime crush. Even though she knows that the person Noah really loves is Alicia, his blood-related older sister and Rachel's best friend... Alicia, beautiful and intelligent, has a congenital heart condition, so Noah's married life is full of lies in order to spend Alicia's meager remaining life with her. Rachel's heart aches with both extraordinary happiness and a sense of guilt... but who is the real "bystander" in this love?

(Source: J-Publishing, translated)