Fan Casting Too Good for This Sinful Earth in Sort by Tropes

A popular and old trope to justify Kill the Cutie. If there is a child of extraordinary beauty, goodness, and innocence in the story, they will invariably die in as unsubtle a manner as possible. The child will be certainly Delicate and Sickly, and frequently a Waif Prophet, whose death will be slow and lingering, giving the child a chance to bid farewell to everyone she loved in a drawn-out drama scene. After she's breathed her last, her loss is mourned by all who knew her— in particularly extreme cases even the Big Bad will be shaken and take a moment to reflect on it— and may serve to re-energize tired or disillusioned heroes to fight on for her cause.