Fairy Snuff (Pixiv Fanbox)

Thousands of fairy clans populate the magical forests of [name undecided], each led by a biologically immortal patriarch (and in rare cases, a matriarch--those tend to not last long). The giants require one daughter per 15 years from each clan, which equates to about one sacrifice per day. The giants do various things to the sacrificed girls. Sticking around and watching a sacrifice is what gave Lily's father the idea to do what he did.