Miumiu is Professor Moshimo's young and beautiful assistant, as well as his fiancée. She can frequently be seen helping her fiancée in his work, especially when she isn't trying to pull him away from it with her affection.
Despite the obviously vast age difference the couple have, it's just as obvious that Miumiu and Professor Moshimo genuinely love and care about each other. One example of such is when she continually pulled Moshimo away from a holo-chat with Robotboy, to make out with him.
She can always be seen wearing a form-fitting kimono. In Season 1 and 2, she wears a black kimono with red stripes, while in Season 3 and 4, it is changed to purple, while keeping the same red stripes.
She's mostly known for being quiet almost all the time (except for two episodes where her voice can be heard). It is unknown why she is always silent, though she isn't voiceless, as we can hear her giggle in Season 1, on the episode "Brother". She doesn't speak clearly until Season 4, where she speaks in the episode "Grow-No-Mo!" and sings in "Cheezy Fun for Everyone".
She appears to be on good terms with Tommy, Lola and Robotboy, while Gus, on the other hand, has only ever been seen frowned at by Miumiu.