What was her appeal? Why was she the most popular?
While K-On was nearly perfect (particularly the second season), I feel like Mio became one of the weaker characters, relatively speaking. Regardless, her boke-tsukkomi friendship with Ritsu worked excellently (and transcended the comedy elements to seem like a genuinely strong bond), but in other ways she was usurped by Azusa.
As to why she was the most popular, the answer is a bit shallower. She was the only character to provide any real fanservice and elicited a lot of moe in her helpless moments and when being bullied by Ritsu (who IMO is a more interesting character).
Mugi is my favorite and my waifu, though.
post *that* image
Please don't sully the Keions like that.
>Why was she the most popular?
Only she wasn't
Most developed body and like >>157482658 said most feminine.
Wow that chart goes from reasonable to complete shit quite fast.