Lum hails from the planet Oniboshi as the daughter of the Invader King. She first arrives on Earth challenging humanity to a game of tag, randomly selecting Ataru Moroboshi as her opponent. When Ataru's triumphant shout following her defeat is misinterpreted as a marriage proposal, Lum moves into his home and declares herself his fiancée. This dynamic becomes central to her story.

Despite Lum's persistent romantic pursuit, Ataru frequently chases other interests. Lum reacts to these perceived betrayals or rejections with intense jealousy, often channeling it through her innate electrical powers to shock him. Her abilities include flight using small wings on her back, generating electrical discharges, and resilience to physical harm. Her signature attire is a tiger-striped bikini and miniskirt ensemble.

Her background as an alien princess surfaces periodically, notably through interactions with her father, the Invader King. He initially disapproves of her relationship with a human but gradually accepts her life on Earth. Lum exhibits a complex personality blending confidence and vulnerability; she openly expresses affection for Ataru while experiencing deep insecurity about his wandering attention. She forms friendships with human classmates, including Shinobu Miyake, navigating both ordinary school life and extraordinary supernatural events alongside them.

Lum appears consistently across the original television series, multiple OVAs, and all theatrical films, maintaining her core traits while exploring different scenarios within the established setting. Later animated adaptations also depict her in the role of her own mother, expanding her familial portrayal. Her character remains defined by the juxtaposition of her alien heritage and her adaptation to human social environments, particularly through her persistent, though tumultuous, bond with Ataru.