Mimmy White is Hello Kitty's shy, polite, and very girly twin sister. Her appearance mirrors her twin's, except she wears a yellow ribbon on her left ear, while Hello Kitty wears a red ribbon on her right ear. The twins share a close bond and often venture together on adventures. In the "Ringo no Mori" series, the apple fairy Pluru guides them to the Mysterious Forest, where they are hailed as "the brave two-legged heroes" destined to save the apple forest's princess.

Mimmy enjoys sewing, patchwork, and home economics, her favorite school subject. She embodies traditional femininity, often dreaming of marriage and aspiring to become a beautiful bride someday.

During the events of "Ringo no Mori to Parallel Town," Mimmy and Hello Kitty plunge through a hole into a parallel world inhabited by humans possessing transparent wings and pointy ears. Within this world, Mimmy vanishes, sparking a rescue effort hindered by the black cat antagonist Akuro.

She belongs to a prominent Sanrio family, including her parents and extended relatives. Mimmy stars in multiple Hello Kitty OVAs such as "Hello Kitty: Santa's Missing Hat," "Growing Up With Hello Kitty," and "Kitty's Paradise," along with various other television specials and films.