Saitou in the first season when he one shots the golem that multiple mages couldn't defeat and he does it using the "Staff Of Destruction", which is actually a LAW, a.k.a. Light Antitank Weapon.
Saito using the Zerosen to single-handedly wipe out Reconquista's entire dragon army.
Saitou goes alone against up against an army of 70,000 bloodthirsty, berserk soldiers, held them off for four Goddamn hours by himself.'' On top of that, he didn't kill a single enemy, only knocked them unconscious.
Just over two years after author Noboru Yamaguchi's passing, it was announced that, after years in limbo, the series will finally see its long-awaited completion. That's right, Yamaguchi is finishing the series from beyond the grave. Granted, he's getting help from still-living editors, but still!