Every 60 years, the heavens conduct a sacred ritual called ETM12. This custom involves selecting worthy Eto-musume—celestial beings representing different animals—to become one of the members of the Chinese zodiac, or Eto-shin. However, since the first ETM12 two thousand years ago, the original batch of Eto-shin reigns with no one being able to replace them. Nyaa-tan is a cat Eto-musume who aspires to become a member of the zodiac in the ongoing ETM12. Fulfilling her ambition requires her to secure 12 seals, one for each Eto-shin. To that end, she must win various types of battles using Sol/Lull—divine energy created by people's positive emotions. This task is not easy however, as her powers as an Eto-musume are far below the abilities of a single Eto-shin. As such, she needs a constant source of energy. But in a chance encounter, Nyaa-tan meets Takeru Amato, a man who has just transferred to the apartment where she is secretly staying. To Nyaa-tan's delight, Takeru discovers that he gives out high quality Sol/Lull—something that sets him apart from most people. With this, the story of Takeru and Nyaa-tan begins. As Takeru supports Nyaa-tan in her dreams, he meets the Eto-shin and begins to uncover a mysterious past. [Written by MAL Rewrite]

Karin, a DNA operator from the future, is on a mission to change the course of History by stopping Junta Momonari from becoming the Mega-Playboy who fathered 100 children and led to the overpopulation of the world. But Junta is no playboy; in fact he is allergic to girls. But when Karin shoots him with the wrong DNA-altering bullet, he starts sporadically becoming the Mega-Playboy capable of charming any woman. Karin must try to restore the situation to normal before the change to Mega-Playboy becomes irreversible. (Source: ANN)

Cinque returns to the land of Flonyard in Dog Days' to resume his duties as the hero of the Biscotti Republic and it's as though he never left! The difference this time is that he's brought two friends with him who become heroes in their own right: childhood best friend Rebecca Anderson, who becomes the hero for the Principality of Pastillage at the urging of their leader Princess Couvert Eschenbach Pastillage, and his cousin Nanami Takatsuki, who becomes the hero for the Galette Lion Dominion. As with the first season though, with so many secrets to be uncovered and mysteries to be solved, will there even be time for the athletic events that these three hyper and athletic teenagers love to participate in so much?

Dog Days takes place in the world of Flonyard, an alternate Earth inhabited by beings who resemble humans, but also have the ears and tails of specific animals. The Republic of Biscotti, a union of dog-like citizens, has come under attack by the feline forces of the Galette Leo Knights. In an effort to save Biscotti, Princess Millhiore summons a champion from another world in order to defend her people. That champion is Cinque Izumi, a normal junior high student from Earth. Agreeing to assist Biscotti, Cinque retrieves a sacred weapon called the Palladion and prepares for war. In Flonyard, wars are fought with no casualties and are more akin to sports competitions with the goal of raising money for the participating kingdoms. Cinque is successful in his role as Biscotti’s champion, but learns that a summoned champion cannot be returned to their home world. The scientists of Biscotti will endeavor to find a way for Cinque to return home, but until they figure something out, he must serve Princess Millhiore by continuing to fight as Biscotti’s hero.