Klein Mü, known as Little My, is a central figure in the Moomin franchise. She is the youngest daughter of the Mymble and sister to the Mymble's Daughter. Little My divides her time between the Mymble Residence and the Moominhouse, where she is treated as family.

She possesses an exceptionally small stature, fair skin, green eyes, and bright ginger hair styled in an onion-shaped top knot. Her typical outfit includes a red button-up smock dress, magenta or grey trousers, a pink ribbon, black gloves, and boots.

Her personality is fiercely independent, abrasive, and mischievous. She exhibits impatience, bluntness, and a disregard for social norms, often using confrontational rhetoric. Despite this brashness, she demonstrates loyalty and protectiveness towards her friends. She actively joins activities with Moomin, Snufkin, Sniff, and Snorkmaiden but voices skepticism about impractical ideas. Her humor is dark, showing a morbid fascination for disasters.

In the 1990 anime adaptation, her background differs: she is unrelated to Snufkin, contradicting the books' canonical half-sibling relationship. One episode depicts her expressing romantic interest in Snufkin. Her independence is evident as she hibernates at the Moominhouse during winter, demanding to be awakened on the first day of spring. She frequently visits the Mymble Residence to check on her sister but consistently rejoins the Moomin family's adventures.

Little My often drives events through her fearlessness. In *Tanoshii Moomin Ikka: Moomin Tani no Suisei*, she accompanies Moomin, Sniff, and others to the Lonely Mountains Observatory to investigate a comet threatening Moominvalley, confronting challenges with boldness and pragmatism throughout the journey.