Lum is an extraterrestrial being from the Oni race, hailing from the planet Oniboshi. She is the daughter of the leader of the alien invaders who attempted to take over Earth. Her most distinctive physical features are two small horns on her head, which are tied to her supernatural powers. She typically wears a tiger‑striped bikini and go‑go boots, and her hair is a vivid cyan shade, a change from the iridescent coloring of the original manga. Her appearance and clothing are heavily inspired by the Japanese thunder god Raijin.

Lum grew up on Oniboshi as a precocious child, attending primary school with Benten, Oyuki, and Ran, a group that frequently caused large‑scale trouble. She later became engaged to a handsome oni named Rei but ended the relationship because she found him dull. When the Oni invasion of Earth began, a game of tag was proposed to decide the planet’s fate. Ataru Moroboshi was randomly selected as the human champion. Ataru managed to win by stealing Lum’s bikini top, and in his excitement he shouted “Now I can get married!” Lum misinterpreted this as a marriage proposal directed at herself. Because engagements are considered sacred on her home world, she accepted and moved into Ataru’s house, determined to become his wife.

Lum’s personality is generally cheerful, laid‑back, and enthusiastic about life on Earth. She is deeply devoted to Ataru, whom she calls “Darling,” and she strives to be an ideal wife, taking care of the household and helping his mother. However, she is quick to anger, especially when Ataru flirts with other girls or when anyone insults or attacks him. In such moments she releases powerful electrical discharges. She is intelligent but remarkably naive about Earth customs, often misunderstanding social situations. Her worldview has been compared to that of a kindergartner, and she frequently speaks with a catchphrase ending in “datcha.” She possesses a strong desire for a stable domestic life with Ataru, often imagining a “sweet home” where they raise children together.

In the story, Lum serves as the female protagonist. Her accidental arrival and self‑declared marriage disrupt Ataru’s everyday life and create the central comedic and romantic conflict. Despite her alien origin, she becomes a fixture of the Moroboshi household and later attends Tomobiki High School alongside Ataru. Her presence draws the attention of many male students, including the wealthy Shutaro Mendo, but she remains unfailingly loyal to Ataru.

Lum’s key relationships include Ataru Moroboshi, her reluctant fiancé; Shinobu Miyake, Ataru’s former girlfriend and a rival; Ten, her younger cousin who often causes chaos; and her childhood friends Benten, Oyuki, and Ran. She also interacts with Ataru’s parents and the other eccentric residents of Tomobiki. Over the course of the series, Lum shows growth in balancing her fiery temper with moments of vulnerability and genuine affection. She gradually adapts to Earth life, although her misunderstandings and impulsive use of alien technology frequently lead to comedic mishaps.

Lum’s notable abilities include flight and the generation of high‑voltage electricity, which she can direct at will. She also has access to various advanced alien gadgets, though her lack of familiarity with Earth often causes them to malfunction or produce unintended results. Her powers are directly tied to her horns: if the horns are removed or if specially blessed yellow ribbons are tied around them, she loses both her flying and electrical abilities and becomes an ordinary girl. She can consume extremely spicy foods such as Tabasco sauce without ill effect, but certain Earth foods like pickled plums can intoxicate her.