Mariel Loughran is a human child living on Earth who lives with an unspecified illness. This condition brings her life into danger multiple times. During these critical moments, she is saved by extraterrestrial beings from the small planet Riruru, including Titila and a group of 225 similarly tiny people small enough to fit in a human hand. Protecting the existence of these extraterrestrial visitors becomes significant for Mariel; she actively guards their secret and prevents other humans from discovering Titila and her group. Her father appears briefly via his voice in one episode.