It was called “Emergence Day”.

The day a mystical portal to another world, a dungeon appeared in the heart of Atlanta. A day when monsters were unleashed on the world. Caught far away from safety, one young man, Luca, finds himself chosen by the immortal Amarath, the dark spirit that presides over the dungeon.

Granted the Black Seraph's legendary power, Luca must learn how to survive in a post-apocalyptic world full of monsters before he, too, succumbs.

(Note: This was previously published under the name Carrion Crow).