Ran, an alien from the planet Uru with traits linking her species to Oni—manifesting pointed ears and sharp teeth during anger—shared a close childhood friendship with Lum, Benten, and Oyuki during elementary school. This bond fractured over accumulated resentments. Ran endured punishment for Lum’s reckless acts and later harbored deep jealousy when both developed feelings for the shapeshifter Rei. Rei chose Lum, who ultimately rejected him for his shallowness, but this did not ease Ran’s bitterness; she blamed Lum for her misfortunes and heartbreak.

Driven by vengeance, Ran arrived on Earth disguised as a human, enrolling at Tomobiki High. Her initial plan targeted Lum’s fiancé, Ataru Moroboshi: she aimed to steal his youth via her innate lip-contact vitality absorption. This failed when Ataru consumed a youth-restoration potion. Ran then pivoted to direct revenge against Lum, deploying black magic, advanced alien tech, and intricate schemes that often ensnared bystanders. These attacks were frequently triggered by sudden, painful nostalgia for their shared past.

Ran exhibits a severe split personality. Publicly, she embodies a crafted "kawaiiko" persona: using high-pitched, feminine Tokyo dialect, referring to herself in the third person (e.g., "Ran-chan is sooo happy!"), and feigning childlike innocence and elegance. Privately or when provoked—especially by reminders of Lum or Rei—she reverts to her true self: aggressive, cynical, and vengeful, marked by Kansai dialect and the rough pronoun "washi." This duality began as a strategy to attract Rei but became ingrained, causing abrupt, overlooked shifts between personas.

Her abilities include youth absorption and restoration through kissing, high proficiency in alien technology and witchcraft for revenge plots, and exceptional cooking—a skill used to retain Rei’s attention. Her recurring arsenal features hammer bombs, a light saber, and self-destructing messenger dolls.

Residing in a parked UFO on Earth, Ran experiences partial reconciliation with Lum as their friendship tentatively revives. She dates Rei, though his interest centers on her culinary skills rather than genuine affection. Shared experiences—like coaching Ryunosuke Fujinami in femininity or joining group activities such as sentō parties—contribute to a gradual, incomplete mellowing of her vengeance. Her name reflects this conflict: "Ran" (蘭, "orchid") symbolizes her delicate facade, while the homophone (乱, "chaos" or "civil war") alludes to her fractured psyche and feud with Lum.