Angel Blade

Nikka is dying of cancer until a stranger provides her with a cure, but it comes at a steep cost: she must become a Seraph, an angelic being with the power to exorcise and destroy demons. With Gideon, the stranger who introduced her to this life, she learns of the battle between Heaven and Hell and about the part she must play to fight the demon horde and destroy Abaddon, the Prince of Demons.
Then she meets Jason, a man with a troubled past who also brings the promise of a normal life, and his offer may be too good to let go.