What was summoned by the hero summoning was something unexpected.

In a world where humans and demons are at war, the human side performs a summoning ritual to call a hero from another world to fight for them. Everyone expected a human to be summoned, but what appeared was something completely unexpected. Through conversations with this unexpected being, the humans come to realize many things. Eventually, in order to end this war, it begins to take action to negotiate with the Demon King as well.