@IJustMadeThisToComment This is actually kind of a thing in D&D because of monsters with this ability, such as the rust monster. An otherwise relatively harmless monster that has nothing much going for it strength wise, but hitting with metal weapons will pretty much ruin them, and it hitting metal armor will do the same there. Your suggestion of punching it is pretty much right for a lot of people, non-metal weapons are a thing too though like a wooden club or staff. Magic might work too, but there's probably magic resistant varieties just to fuck with the players even more (there are a number of entries in the D&D monster selections that are specifically designed for letting DMs be complete assholes).
last panel : why does she punch the old man ? he did not do nothing wrong .
maybe she wants to take it out on someone , but she cant punch the slime , the pixie , or the mc ( her lover ) , so she punches the old man , lol .
it reminds me of this scene : while 1 person is opening a chest , 3 persons are yelling while standing far away because they are afraid of bombs , poison gas , ...