@Cephi
"Level 300+ doesnt seem much in this world when lvl 37 can fully block your attacks."
The demon didn't block the magic, it was the shield. It's a powerful magic item, like the magic cannon the demon tries to use. The spell Satou uses; Magic arrow, is a beginner level spell. If it was D&D it would be the equivalent of a 1st level spell like magic missile. A level 300+ wizard can cast a lot of them, and they'd do a helluva lot more damage than one cast by a 1st level, but it's still a level 1 spell. The shield nullifies all beginner level spells. A D&D example would be a magic item that nullifies all spell effects of level 1-3.
This isn't the first time he runs into this problem, nor will it be the last time. It's the reason why he's been so kee on learning spells, especially intermediate and higher level spells.