Gorgoneion

The Gorgoneion is a grimoire in Campoine.

Summary
A grimoire won by Godou Kusanagi after he defeated Erica in a demonstation battle, it contains the power of the Snake and is sought by the goddess Athena. It's hinted that it was stolen from Athena by Verethragna, it's also hinted that it's a weapon in the shape of a scythe. However, it turns out to be the last piece of Athena as once she obtains it, she returns to her original form.

In the anime, after Athena's defeat at the hands of Godou, the Gorgoneion fell into a well. From it came Athena's Snake, which assumed the form of Metis.

Trivia

 * Gorgoneionwere real items in Ancient Greece, and acted as protective amulets.