A Corpse is Buried Under Sakurako's Feet.

桜子さんの足下には死体が埋まっている

Sakurako Kujou is a brilliant, reclusive woman in her mid-twenties who cares about almost nothing except bones, and would spend all her time alone in her house full of skeletons if not for her constant companion, high schooler Shoutarou Tatewaki. Why she keeps him around isn't clear, but one thing is: whenever the two go out together in Asahikawa, Hokkaido, they are likely to stumble on a human corpse. This light novel is the original source for the manga and anime adaptations, the latter titled Beautiful Bones: Sakurako's Investigation.