A fortress city, seized by demons. To save its people and set the city free, the demon-hunting knight Rein McWell sets out for it alone.

She fights with a katana, and with a darkness that dwells within her. The very power she relies on to fulfil her mission is also the power that is consuming her.

With every battle, her resonance with the dark grows deeper. And alongside her resolve to save the people, Rein slowly begins to crave that power.

Will she master the darkness and see her mission through? Or—