Feast of Samael (The Devil's Trials) by Stephanie Gluck

The devil was thrown from the old world and, bypassing hell, he landed in Kaida. He dragged seven corrupted angels with him, and they rose as the embodiment of the deadly human sins. Beneath their rule the world was ravaged and reborn. The angels encouraged and punished a sinners' nature and their influence, demons and temptation killed in equal measure. The devil quickly grew bored. Once a decade he offered the humans a series of trials. Face a challenge from each of the seven deadly sins and triumph, and in return he would grant every benefit of the devil’s favour, including immortality. Pure desperation pushed Octavia Nox to enter the devil’s trials, she just wants to survive another day. All too soon she is forced to confront the first of the sins. Where she must face the reality that she could be a sinner at heart, and these sins may just eat her alive.