Cosmo is generally described as a beautiful alien girl with plant-like features. She has green, leafy hair, royal blue eyes with a single eyelash, and tan-colored skin. Along with a green dress with a white petal like skirt with green tips at the end and uses them as a parachute from falling down. She wears white tights and green ballet shoes.
Cosmo is a kind and gentle character, though she often feels guilt when she feels useless and couldn't save her friends. She also seems to suffer from a low self-esteem issue, often calling herself "unworthy" or blaming herself for the hardships that she and her friends had to endure. Cosmo also dislikes violence, but acknowledges that fighting is sometimes a necessity, although she herself is unable to fight. Cosmo can be somewhat clumsy, but she is also quite resourceful; she also has a penchant of getting into trouble.