Tartan is the younger sister of the main character, Nontan, and a kitten distinguished by a blue ribbon. She first appeared in the 2001 picture book *Nontan Imōtoīna*. Her name originates from the author's son's sister, and the inversion of the actual sibling age dynamic between the book characters and the author's own children resulted from a mistake regarding which child was older.

Tartan is characterized by a fondness for mischievous behavior and a particular liking for onis, a type of creature from Japanese folklore. Following her introduction, she resides with Nontan in his house, which features a flag on its roof. In animated adaptations, the character appears only in the 2002 television series.