In order to stop the war with the demon race which took everything from him, adventurer Dave tries everything to put an end to it. He's aided by his fierce but eccentric guild members, and his childhood friend Kenneth, who is directly working for the King as a Court Scientist. He's the mastermind behind their missions, and one day, an unprecedented opportunity arises: To take Precia, the heir of the local demon lord, hostage!

But Precia is still just a child! Until their hostage can be bartered away, Dave takes it upon himself to hold her captive at their guild's headquarters, allowing Kenneth to study her. Dave's deep-rooted hatred for demonkind isn't helping. Gradually, though, the little demon princess warms Dave's bitter heart, Soon, he acts like the loving father Precia never had but then diplomacy begins and Dave has to make some tough choices, that will decide not only Precia's fate but humanity's fate as a whole.

Can the bond that forms between them end the war?