The Last 9 Days of Anastasia

The manga is set in a fantasy world where the Church of Light and the Church of Darkness have waged an unending thousand-year war, though the Church of Light seems to finally be losing. In desperation, the Church of Light magically summons a hero to their side. Though powerful, the hero is burdened with a terrible destiny: that she will die in nine days. Now the hero and her companion priestess go on their short journey as the last hope of the Church of Light.

(Source: ANN)