Pequeña My, called Little My in English, primarily lives at the Mymble Residence with her sister, the Mymble. Before the series starts, she stayed at Moominhouse and hibernated there one winter while the Mymble was away, establishing her early link to the Moomin family.

She possesses a fiercely independent, determined, and occasionally aggressive personality. Her direct, action-oriented approach shows little regard for conventional respect or social norms. Despite her brash and disrespectful demeanor, she demonstrates loyalty and functions as a reliable friend within the group. She exhibits mischievous tendencies, once hiding in a cooking pot during hide-and-seek to startle Sniff upon discovery.

Skepticism surfaces when discussing fantastical concepts like the Snork's Flying Ship. She readily engages in playful activities, such as a competitive cloud-riding game where she deliberately collides with Sniff until he falls off, securing victory. She expresses visible disappointment when magical phenomena like disappearing clouds interrupt her enjoyment.

In one incident, she witnesses Moomintroll transform into a grotesque creature after hiding in the Hobgoblin's magic hat. She observes calmly as others panic, later seeing Moominmamma recognize her son, breaking the enchantment and restoring his form.

She actively participates in retrieving the discarded magic hat against Moominpappa's instructions, hiding it in Moominhouse's cellar. This decision leads to consequences when she tosses a twig into the hat, causing a massive tree to grow and rapidly consume the house. She promptly reports this development to Moominmamma.

Her relationship with Snufkin differs from the literary canon; while the books establish them as half-siblings, the anime adaptation removes this connection. In one episode, she displays romantic interest in Snufkin, further distinguishing her anime portrayal.

She occasionally collaborates, like joining Moominmamma on an adventure to locate rare ingredients for a special dish, demonstrating her capacity for cooperation despite her typically self-reliant nature.

Throughout the series, she maintains characteristic fearlessness and a pragmatic outlook, often serving as a catalyst for events through her actions or commentary. Her interactions consistently highlight her distinctive blend of mischief, independence, and underlying loyalty.