Mabase's newest resident, an extraterrestrial investigator for the Galactic Space Police Brotherhood. She becomes the Nandaba household maid while working to find Atomsk, the most powerful space pirate in the galaxy.
Haruko Haruhara (ハルハラ・ハル子, Haruhara Haruko) is an energetic, spontaneous, hot pink-haired girl, and investigator for the Galactic Space Patrol Brotherhood/Stellar Fraternity. She claims to be 19 years old, but it is impossible to know if this is the truth. In the first episode, she runs over Naota with her Vespa and hits him on the head with her guitar. Soon after she's hired by Naota’s father, Kamon, as a house maid. She is called Haruha Raharu (ハルハ・ラハル) by Amarao; this may be another alias, however.
Haruko is highly eccentric, violent and unpredictable. She is the most erratic character in the show and the things she does and says often make very little sense. This is largely an act, though, to mask her true nature. While her relations with Naota and her battles with Medical Mechanica drive the plot, Haruko's true goal is Atomsk's power, and she will stop at nothing to get what she wants. She manipulates Naota to this end and is furious when her plan backfires, but despite it all the boy seems to have grown on her enough that she allows him to kiss her and parts with him on friendly terms
Haruko is a tall woman with a light complexion, medium length pinkish hair cut into a flare and yellow eyes. Her usual outfit is a bright red coat, black pants, white boots, and white scarf. She wears many other outfits in the series, but one fashion accessory she is never without is a large metal bracelet on her left wrist. The bracelet acts as a kind of radar device, reacting to N.O. power and letting her know where MM robots and/or Atomsk might be.
Naota- Haruko first meets Naota when she runs him over with her Vespa and proceeds to beat him in the head with her bass. He thinks she is insane, especially when she continues to follow him and eventually gets a job working as a maid in his house. He tends to be very outraged at her wild behavior except when she does something cool or impressive. Over the course of the series, he develops feelings for her, which he reveals in the final episode. However, to Haruko, Naota is nothing more than a tool in her grand plan-- all she really needs from him is his head, which is an N.O. channel from which Atomsk can be freed. She merely manipulates his feelings, since she doesn't care much for anything or anyone, just her own desires. However, the boy eventually seems to have grown on her enough that she allows him to kiss her and even offers to take him with her before noting he is just a child. She parts with him on friendly terms, leaving her bass for him.
Mamimi- Mamimi and Haruko do not have much in the ways of interaction, but as Naota's personality changes because of Haruko, Mamimi finds herself liking him less and rejecting him more. While Mamimi never shows jealousy or anger toward Haruko directly, she cuts off all ties with Naota and leaves completely in the final episode, even though Haruko is gone.
Kamon- Naota's father is interested only in his wants. His main desire is the lovely Haruko, who would make the perfect young bride. Because Kamon pines almost blindly for her, Haruko is easily able to use him for her own motives.
Shigekuni- Naota's grandfather also thinks Haruko is quite the babe. While he is too old for her and doesn't pursue her, he still finds her arousing and thinks her baseball skills are intimidating.
Canti - Canti is the robot that pops out of Naota's head in the first episode because of Haruko hitting him with the bass. Thinking that by hitting him, she will free Atomsk, she hits Canti, only to break the conection between him and Atomsk (thus, he turns from red to blue). He comes an obedient, helpful robot afterwards, and listens to both Haruko's chore commands and her orders when engaged in battle with other Medical Mechanica robots.
Miyu Miyu- While Miyu-Miyu (Naota's cat) tends to be unfriendly, he allows Haruko to play with him quite a bit (and rather roughly!) Being another male in the Nandaba household, he probably is attracted to her too. Haruko uses his as a method of communicating with the mysterious Fraternity which she is a part of.
Amarao- Amarao was Haruko's Naota in the past, and thus is trying to keep Naota from ending up like he did. However Naota has a much stronger channel connection than Amarao does, so Haruko actually finds him of use, unlike Amarao. Judging by the way Amarao acts around her or while talking about her, it is hinted that he has some feelings for her, just as Naota does. However, she's an alien, and a troublesome one at that, so those feelings are diluted by his anger towards her, what she did to him, and the trouble she causes. Haruko finds Amarao to be completely weak and pathetic, and doesn't fail to let him know.
Atomsk - While Haruko is willing to chase him across the galaxy, Atomsk seemingly has no interest in her. She is supposedly in love with him, but knowing Haruko's personality, she is more likely in love with his vast power. When Naota is merged with Atomsk, Haruko goes into a rage and yells "Nobody's going to eat that but me!" This most likely refers to the fact that, in order for Canti to gain Atomsk's power, he eats Naota (who has the N.O. channel connection). Haruko must similarly want to eat Atomsk to merge powers and identities. When Atomsk is freed, he dashes off at a brilliant speed, leaving Haruko behind. She is upset that she's lost him again, but she simply hops on her Vespa and again takes up the chase.