If he can just do magic and create fireballs etc. Just by imagining them, why not just create small sphere of water compress it to a really small size and pierce through everything? They really should explain more about the magic in their stories (unless they did in this story, I skipped some text but I saw MC saying something like imagine and create, not sure if I remember correctly, but if not then I was just talking about all other stories like that too) also it doesn’t have to be water he can create from something else probably.