Juushin no Katana

The Rat, the Ox, the Tiger, the Rabbit, the Dragon, the Snake, the Horse, the Goat, the Monkey, the Rooster, the Dog, and the Pig. These twelve tribes, each boasting their own special powers, battled for hegemony over the nation until the Emperor, tired of these endless wars, instead proposed a "festival"—5v5 proxy battles for which each tribe must send a "beastblade" to fight on their behalf. Princess Ibusuki of the Rabbit tribe, the weakest clan of all, was searching for her own champion to whom she could entrust the fate of her people when she came upon Hijimaru of the legendary Lion tribe. Little did she know that this encounter would mark the beginning of something far greater! Welcome to the fantastical tale of the zodiac struggle!

(Source: Kodansha USA)