The World's Strongest Rearguard: Labyrinth Country's Novice Seeker, Vol. 8 (manga‪)‬

Arihito and his party arrive in District Seven with their reward from the Shrieking Wood in tow: a curious black box. But just as they’re about to open it, Ariadne appears with a warning. Sealed inside the box, she says, is a dangerous, sentient weapon capable of wiping them all out or providing them with great power—if they can manage to control it. Arihito isn’t one to back down from a challenge…but will a weapon of the Hidden Gods prove too much for his party to handle?