He is seen by the characters to be super attractive, but he's also super clumsy and humble. Ordinarily, there is an expectation that attractive people are graceful and not so humble. That he goes against the expectations makes him cute and likable. And that he is honest about his quirky eyesight and sincere in how he treats people also makes him likable. That's just my experience, though.
Same with people around me, but society at large has these ideas about how people should be based on what they look like or whatever. Then, generally speaking, there is an expectation built on that. But people violate those expectations all the time. Sometimes in ways that aren't good, but sometimes in ways that are. When it's good, it's very moe. It just happens to be more exaggerated in manga.
Why is Akane's sooooooooo popular..?? (Just curious. NO HARM MEANT)