Ryuu no Nieyome: Shiitagerareta Shoujo wa Unmei no Tsugai toshite Aisareru

Despite being born into a renowned family, Suzu is called a "useless, nameless outcast"—and is treated as such for having no spiritual power. Curses eat away at her body from being forced to act as a poison taster for her younger half-sister. Her miserable life takes a turn when, during the priestess selection ritual, she is chosen by the Azure Dragon as his one and only cherished mate. A cruel god meets a nameless, oppressed girl in this Japanese-style Cinderella fantasy romance!

(Source: Square Enix)