Haruko Haruhara, 19 (or so she claims), is an energetic, spontaneous pink-haired girl from outer-space and investigator for the Galactic Space Patrol Brotherhood/Stellar Fraternity. Mamimi observes that she looks at least twenty years old but, considering that she is of an unknown alien species, neither Mamimi nor the viewer has a relevant frame of reference. She rides a yellow Piaggio Vespa (and is also known as The Wasp Woman, a pun on the word Vespa, which means wasp) and wields a blue, upside down strung, right-handed (but she is left-handed) Rickenbacker bass guitar model 4001 (similar to the 4001 used by Paul McCartney, whom she mentions in Episode 5), with a pull-cord motor on the back, as a bizarre weapon of sorts. Her guitar is able to shoot bullets, act as a rocket launcher, fly, and is used several times to open an N.O. channel in Naota's forehead.

She becomes the Nandaba household's maid and plays on a rival team of the Mabase Martians seemingly for extra money, but in fact to knock a satellite out of Earth's orbit with the baseballs she hits. She has also apparently had past relations with Amarao, most likely similar to her relationship with Naota. This mysterious character is the catalyst for FLCL's entire plot. She is called Haruha Raharu; this may be another alias, however. Haruko has connections to the Nandaba family cat, Miu Miu. The cat serves as a "walkie talkie" to her superiors. The cat does not speak (besides its "meows" and grunts) but it is obvious that Haruko is getting some kind of reply as her conversations with Miu Miu are reminiscent to that of a telephone conversation.

Naota calls Haruko Haruhara "Haruko," Kamon calls her "Haruko-san," and Mamimi refers to her as "Haru-san." Amarao, who believes her real name to be Haruha Raharu, refers to her as "Raharu."