Mumu Momoyama

A roguish person who loves his own cute self. A boy with an abnormally cute face; somewhat narcissistic and into his own looks. His looks are so girly that Mika-chin names him as the cutest around. He and Mimi get off to a bad start but gradually become friends and develop an awkward, self-conscious relationship. He's selfish and mischievous, but no match for his firm, strong older sister. He comes from an affluent family. He likes Mimi's dog, Chiffon, and is fond of aosuji ageha (common bluebottle) butterflies. His "Kigurumimi" mascot character is a rabbit. He likes to play video games and tease Mimi.

His special skills include looking cute and pulling pranks.

(Source: Wikipedia, translated)