I was wishing that MC had dark magic. I'm being extremely delusional here but maybe he has such weak water magic because it's not his main element, it was mentioned that a main element is the one you're best at but you can still use a small amount of an other so maybe he has dark magic it's just that he thought he had water. As I said that's just me being delusional I love characters with dark magic.
Either that or the magicless dude actually has dark magic but is ashamed of it and is hiding it that's why he was so serious about the subject of it because he has internalised hate for it since it's seen as evi.
Nehehehe
