this is for new zodiac, after 1000 years (?) zodiac is revamp or something and all animal have to battle to get places in the new 12 zodiac...
Every 1000 years all 100 participants and the 12 actual Zodiac will have a chance to be the New 12 Zodiac. The Rank depends on the Happiness Meter of their Master.
http://www.mangago.zone/read-manga/eto_royale/nbt/0eb6aeaa8a3675f6/Vol1_Ch1/48/
*Oh and there's a time limit.
http://www.mangago.zone/read-manga/eto_royale/nbt/0eb6aeaa8a3675f6/Vol1_Ch1/22/
Wait, what? So he's already part of the 12 Zodiacs but he still participates in the battle to become one of the Zodiacs? o.o I'm confused.