Carter and A Demon

After the world ended and demons took over the earth. Humans had no choice, but to do everything to find a way to fight back.
Hale Carter was part of a demon fighting organization called the Seraphims. Though his past held dark secrets and scarring memories, Carter worked and fought harder than most. After reaching the highest rank of the Seraphims, his luck seemed to be always against him.
When his life is almost up, a demon appears and offers him a deal. Desperate to live, Carter accepts ready to lose his soul to keep fighting, but the demon has other plans for Carter.