The Youngest Has Much To Hide

Story

Amid the chaos of war, young Rubian realizes a shocking truth: she’s trapped in a novel where the hero dies suddenly, plunging the world into disaster. Luckily, fate leads Rubian to enter the hero's household—giving her the perfect chance to stick close, prevent his death, and leave once the crisis passes. Yet the warmth and affection she receives from his family are unlike anything she's ever known, making it harder to remember that she’s there to stop a tragedy… not start a slice-of-life!

Synopsis via AniList (English).