- Fridge Logic:
- In my opinion, his fighting ability is part from natural talent and caused from watching dream which a woman ,his mother, killing dudes left and right and get killed in return. It reduces some of his empathy and all of hesitation to kill. First wrestling lesson? He goes berserk, not giving his opponent a break. First Sword lesson? He sees the mysterious woman amazingly using sword in his dream, so no problem to use it in-universe. His first real duel? He has no hesitation to kill, currently skilled sworman himself, He has no hesitation to kill, knows his opponent will try to slash him In the Back, and He has no hesitation to kill.
The only problem now, how a child bookworm who spends his childhood life reading books has enought strength to punch a bully, said bully has no chance to fight back while logically his punches can't really hurt and properly moves sword the way he wants, he nearly beat the teacher at first try. The first real fight has no problem as he trained sword several years in the village and reasons cited above. The only explanation for his body's strength apparently those scrolls must be really heavy.