Eto✿Royale (干支✿ロワイヤル) is a manga series by Ritsuhiro Mikami. It was serialized in Asuka (Monthly).
One day, an ordinary high school girl by the name of Ichika Kotobuki saves a dog on the verge of death on the side of the road. However, all of the sudden, the dog transforms into a human. As a consequence, Ichika gets dragged into an event that runs once in a thousand years known as "Eto Battle"!