Jūni Taisen

Jūni Taisen (十二大戦, lit. "12 Wars") is a light novel written by Nisio Isin and illustrated by Hikaru Nakamura. It was published by Shueisha on May 19, 2015. It is a prequel to one-shot manga titled Dōshitemo Kanaetai Tatta Hitotsu no Negai to Wari to Sō demo Nai 99 no Negai (どうしても叶えたいたったひとつの願いと割とそうでもない99の願い). The novel is licensed by Viz Media and will be released in hardcover in October 2017. An anime television series adaptation by Graphinica premiered on October 3, 2017.

Plot
In a city of half a million people who have all been removed, 12 of the deadliest mercenary warriors with the names and attributes of the 12 Chinese Zodiac animals are pitted against each other in the 12th Zodiac Tournament which takes place every 12 years. Each warrior must swallow a poisonous gem, which will begin to kill them after 12 hours. To be granted any one wish of their choosing, the winner must retrieve all the gems from the other competitors before the deadline.