It is about humanity, from a world with medieval fantasy style heroes, being brought to edge of extinction by Demons, their "Natural Enemy". After everything they do proving to be for nothing against the Demons, the last thing they attempt is trying to summon humans from other worlds for help, but it turns out humanity from the other worlds are also facing extinction from their own natural enemies and now all their worlds are mixed into one.. Latest chapter showed what their enemies were and the current plan is to make the enemies fight each other. Only has four chapters out right now and it's monthly, so it might take some time to see where this goes.