I'm saying it's a possibility if it turns out they come every month. Even if they do and it is a ritual, it does not mean it would be for good. We do not know what would happen if there is a creature for each zodiac, but if they are all like this we likely won't have a choice in fighting them lest the city fall into ruins.

Unfortunately we don't have enough information for anything concrete. Not until another being such as this shows up. For all we know this could have been the only one.