Masami is a small, white cloud. Her body is always wiggling for some reason, possibly because she's full of water, like real clouds are. When Masami gets mad or sad, she turns gray and begins to cry, causing her tears to fall from under her like a storm cloud. In The Party, it's also shown that she can fire thunderbolts when she's really mad.
Being the daughter of the owner of the Rainbow Factory, Masami is very rich and also a bit of a snob. She has a smug sense of superiority to her fellow students, which is why she's seen pretending to like Darwin in The Pressure, since having a real boyfriend was seen as impressive by the other girls who all had fake boyfriends. Masami is also arrogant, as seen by her strong dislike of Molly's Treehouse, which she thinks is really boring; that could mean that she's got fancier things at her home. She is also somewhat vain, since she hates getting her hair wet and she sees herself as being better than most of the other girls. In addition, she threatens to fire the parents of anyone who disagrees or annoys her. When she gets angry, she turns grey and zaps the person who angered her.
Contrary to popular fan opinion, Masami actually doesn't like Darwin as a boyfriend. In The Pressure, she was only pretending to like him to impress the other girls.
Masami has been said to have an "unrequited" crush on Alan, which may cause problems between herself and Carmen in the future. It is unknown why she's got the hots for him, though it may have something to do with the fact that Alan is considered the most attractive boy at Elmore Junior High.