The Greatest Demon Lord Is Reborn as a Typical Nobody, Vol. 3 (light novel)

Right in the middle of a class trip, Ard and his crew are blasted to the past by a self-proclaimed "god." Though skeptical of their motives, they find themselves making the most of their time-traveling adventure and joining the army as valiant soldiers to enlist the help of Ard's past self. With another entity claiming to be the "Demon Lord" and mysteries abound, things just keep getting stranger and stranger!