Combatants Will Be Dispatched!, Vol. 4

A month has passed since the cease-fire with the Demon Army, and with the
teleporter online, Kisaragi has sent a mutant to help this invasion get back on
track. But their plans are derailed once again when Six is dispatched on a
diplomatic mission to Toris for water crystals that will relieve the kingdom of
Grace from its terrible drought, a problem he caused in the first place by
changing the rain-making artifact's password to something that can't be printed
on the back of a book. Is Six really the right man for the job...?