Juni Taisen: Zodiac War (manga), Vol. 1 : 1

Twelve fighters enter, one fighter leaves—who will win the 12th Zodiac War? Every 12 years, 12 fighters take the form of the Chinese zodiac and engage in a battle royale. With their strength and mysterious powers, they fight to the death and the sole survivor is granted the ultimate prize—any wish. Eleven of the twelve fighters have gathered, and everyone awaits the final contender—Boar. She is strong, confident and a favorite to win the twelfth Zodiac War. However, this time, the rules have changed! The battle is limited to an abandoned city and all of the contestants are forced to ingest a deadly poison. Monkey tries to call a truce, but before she can the floor explodes, scattering all the fighters. Despite the chaos, one thing’s for sure—only one will remain standing.