Kindred Spirits

Victory comes at a price.
Exiled to Earth, Mina bears the weapon she stole from Satan, preventing him from destroying the angels of light. Despite this, Spirit's Bane weakens her with pain when she uses her Gifts to protect those under her care.
Meanwhile, the Council of Light confines Allister to the Heavens. They fear what Satan will do if he captures the Kindred Spirit Pair. Allister knows they are stronger together, but even if he defies the Council by going to Earth, there's no guarantee he'll reach Mina before Satan's minions.
If Allister and Mina cannot defeat Spirit's Bane swiftly, precious souls will be lost in the coming conflict.
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This book can be read alone, but it would probably be much more powerful (and sensible) if read after Guardian Angel Files Book 1: Spirit's Bane. The series is written in a style reminiscent of C.S. Lewis's Screwtape Letters. The series is available as ebooks, paperbacks, or audiobooks performed by Reuben Corbett.