Kusanagi Godou is entrusted with a stone grimiore by his grandfather to deliver to its former owner, an old friend, in Italy where he encounters supernatural happenings. Meeting the beautiful knight, Erica Blandelli, he is drawn into the battle between rogue gods, and uses the power of the grimiore to defeat the Persian god of victory, Verethragna, gaining his powers, becoming a god slayer, also known as a Campione.

Godou wakes with an unexpected guest in his bed, a guest that is here to stay.

Athena has come to Japan looking for Medusa and for that Godou will have to die, again.