Haruko & Nandaba 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.
Haruko & Samejima Mamimi
Mamimi is a poor, cigarette-smoking high school student whose only close friend (and outlet for sexual frustration) is Naota, since his older brother Tasuku, her boyfriend, moved to the US. 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.
Haruko & Nandaba Kamon
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.
Haruko & Nandaba Shigekuni
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.
Haruko & Kanchi
Kanchi 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 Kanchi, only to break the conection between him and Atomsk (thus, he turns from red to green). 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 Meccanica robots.
Haruko & Naota's ClassmatesNinamori Eri - Eri has feelings for Naota in the beginning of the series, which makes her jealous of Mamimi and to a lesser extent, Haruko.
Gaku - Gaku is very much attracted to Haruko and is appalled by her kissing habits... so he wants a kiss from her too!
Masashi - Masashi is more or less indifferent and more interested in the rumors surrounding her.
Haruko & 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.
Haruko & Amarao
Amarao is a special agent who knows about (though never reveals fully) who Haruko really is. He too has an N-O channel connection, but very weak, because he himself doesn't have much inner strength. He was Haruko's Naota in the past, and thus is trying to keep Naota from ending up like he did. The difference is, 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, he probably has some feelings for her, just like Naota does. However, she in 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.
Haruko & Kitsurubami
While the two never quite interact, Kitsurubami is impressed by Haruko's powerful female dominance, as seen in episode 4 (she gets a nosebleed along with the rest of the Bureau staff while watching Haruko pull a guitar from Naota's head).
Haruko & Atomsk
Atomsk is a most-powerful alien known as "Kaizoku-Ou" (Pirate King). While Haruko is willing to chase him across the galaxy, he 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, well, in order for Kanchi to gain Atomsk's power, he eats Naota (who has the NO channel connection). Haruko must similarly want to eat Atomsk (or have him eat her? He's pretty big) 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 begins the chase again.