Casebook of Kurumi Tokisaki, Magic Detective (light novel) — Koushi Tachibana

Kurumi Tokisaki, a college student with a dark past, works as a detective specializing in crimes involving magical artifacts. A magic bullet fired from an impossible angle; a living doll mixed up in a series of comas; an absurdly expensive meal said to restore one's youth; and a doppelganger spotted at an all-girls' school after an attempted suicide. These artifacts make the impossible possible, but Kurumi won't let that stop her from solving the case!