Dog Days is set in Flonyard, an alternate Earth populated by beings who look like humans but also possess the ears and tails of specific animals. The Republic of Biscotti, a union of dog-like citizens, has been attacked by the feline forces of the Galette Leo Knights. To save Biscotti, Princess Millhiore summons a champion from another world to defend her people. That champion is Cinque Izumi, an ordinary junior high student from Earth. Cinque agrees to help Biscotti, retrieves a sacred weapon known as the Palladion, and prepares for war. In Flonyard, wars are fought without casualties and resemble sports competitions, with the aim of raising money for the participating kingdoms. Cinque succeeds in his role as Biscotti’s champion, but discovers that a summoned champion cannot return to their home world. The scientists of Biscotti will try to find a way for Cinque to go home, but until they figure something out, he must serve Princess Millhiore by continuing to fight as Biscotti’s hero.