Just a silly guy. Mio is known to be playful, joking, care-free, and often times facetious. It's difficult for him to stay serious in serious situations. All he knows is being silly and treats a lot of things lightheartedly, often to the frustration (or relief) of others. Some may consider him a breath of fresh air, while others find him annoying and irreverent. He acts like he doesn't care much what others think of his personality or his behavior, but perhaps it is just that... an act.
Because of his species, he does have a habit of imitating others, intentional or not. He picks up the quirks and phrases of others, especially those he spends a lot of time with. He is also very animated and expressive, using a lot of hand gestures among other body expressions.