I'm the Hero's Sister, but I'm Cross-Dressing as a Stand-in for My Brother Who Eloped with the Holy Maiden

I am waiting for the return of my twin brother, who departed from our village as a hero. One night, a female knight who is a member of the hero's party visits me, avoiding the eyes of others. It turns out that my brother has abandoned his role as a hero and eloped with the Saint. All members of the hero's party are searching for the hero and the saint by dividing up the work, but the disappearance of the hero—humanity's hope—must not become known to the people. For this reason, she has come to ask me to become the hero's body double.