*MC attacks a dragon*
Trash readers: "Go, MC, kill the dragon!"
*Dragon transforms into a little girl*
Trash readers: "How can you hit the dragon, MC?! Can't you see she's just a little girl?! Die, you piece of shit!"
These people wouldn't last a year in a fantasy setting, or in a war zone where people exploit children (e.g.: Vietnam, Afghanistan, etc.) to bomb their enemies.
That's why there's training, I guess. Even though it was common sense that no matter what shape it takes or what language it speaks, that little girl is a monster.