Dog Days takes place in the realm of Flonyard, an alternative Earth populated by individuals that resemble humans but also have the ears and tails of other animals. The feline warriors of the Galette Leo Knights have launched an attack on the Republic of Biscotti, a union of dog-like residents. Princess Millhiore calls a hero from another realm to protect her people in order to rescue Biscotti. Cinque Izumi, a regular Earth junior high student, is that champion. Cinque agrees to help Biscotti and collects a sacred weapon known as the Palladion before preparing for war. In Flonyard, wars are waged without fatalities and are more analogous to sporting events with the objective of collecting funds for the kingdoms that participate. Cinque is a person.