Lan (Ran) is an alien girl of unspecified race who appears as a major character in Urusei Yatsura. She was created by Rumiko Takahashi, who named her "Ran" for its double meaning of "orchid" and "civil war," reflecting the character's sharply divided nature. Her design incorporates pink, cloud-like curly hair, fangs, and pointed ears, tying her visual to both the concept of a gaki, a hungry spirit in Japanese Buddhism, and an oni.

During childhood, Ran was best friends with Lum, an Oni alien, and they attended elementary school together alongside other alien acquaintances Benten and Oyuki. However, Ran frequently suffered harm or trouble because of Lum's carefree and irresponsible behavior. The two also shared a romantic interest in the shape-shifting alien Rei, who eventually became Lum's fiancé. These experiences built a deep resentment in Ran, transforming their friendship into a one-sided rivalry. She travels to Earth seeking revenge against Lum, enrolling at Tomobiki High School while pretending to be human. Her initial plan is to steal Lum's fiancé, Ataru Moroboshi, and kiss him to drain his youth and vitality through a vampiric ability she possesses. When that attempt fails due to Ataru accidentally consuming a youth potion, Ran shifts to targeting Lum directly with elaborate schemes for retribution, often dragging everyone around her into the chaos.

Ran's personality is bipolar and outwardly deceptive. In public she appears sweet, childlike, and elegant, but this facade hides a cynical, vengeful, and obsessive nature. She can switch from friendly to cruel and aggressive in an instant, with her anger typically triggered by reminiscing about past grievances. Despite her mean streak, she is an excellent cook and keeps her own spaceship parked on Earth, always hoping that culinary skills might win Rei's heart. Over the course of the series, Ran becomes entangled in many abnormal and otherworldly situations alongside the rest of the cast, such as trying to teach Ryunosuke Fujinami how to be more feminine or preventing Ataru from crashing a party. While her primary motivation remains revenge against Lum, her presence adds chaotic energy and comedic conflict, and she occasionally joins in group adventures, such as taking a vacation with Lum, Benten, and Oyuki on Neptune. Her notable ability is draining the life force of others through a kiss, which she can also reverse, and she carries a deep-seated bitterness that drives much of her behavior.