The Campione Wiki!
The official source for as much information on Campione as we can scrape up.
A harem love comedy plus magic battles. Kusanagi Godo is a 16-year-old high school boy, who once killed the god "Verethragna" and acquired the title of "Campione", or god slayer, when he was 15. Erica Brandelli is a 16-year-old Italian girl, who is a "Great Knight" of the magic society "Bronze Black Cross" and had fought together with Godo to defeat Verethragna. Godo doesn't like fighting but his title of "Campione" makes him get involved in battles against other Campiones and uncontrollable gods.