Combatants Will Be Dispatched!, Vol. 4 (light novel) — Natsume Akatsuki

A month has passed since the cease-fire with the Demon Army, and now that the teleporter is online, Kisaragi has sent a mutant to help the invasion get back on track. But the evil organization's plans are derailed once again when Six is dispatched on a diplomatic mission to relieve the kingdom of Grace's terrible drought-a problem he caused by changing a rainmaking artifact's password into something that can't be printed on the back of a book. Is Six really the right man for the job…?