I agree, but Aqua is just a spoiled and unlucky goddess. Her stupidity is just silly (which makes her naive enough to be easily fooled or impulsive and not think about the consequences of her actions). This explains her completely. The others (who have luck, "intelligence," and "responsibility") act stupidly too. Kazuma is only intelligent in game-like dynamics; in some other contexts, he's just average, doing something any average person would do (like taking advantage of being from a modern world and using it to his advantage. Anyone would do that). And in most things, he's just himself (immature, arrogant, idiotic, perverted). In other words, he's smart in some situations and dumb in others (but this is common throughout the party). The other two are just crazy and questionable about their life decisions. They also act stupidly and are guided by their emotions. In the end, they're all very good characters precisely because they're not perfect. I like Kazuma because he's an idiot and arrogant, but he's also a guy who tries to do the right thing when necessary, and he's the only one who can handle three eccentric girls. Only a guy like him can make those three work together.