Haruna is a very kind, patient and understanding girl. More than most other girls in the series, Haruna has always known about and loved Rito's positive traits, despite also being a frequent victim of Rito's perverted clumsiness. Haruna first took notice of his existence when he won the school festival for his class, and she has realized and remembered that he must be a kind person since she noticed him taking care of the flowers at school when they were neglected by others. When the plants in the school garden got ruined, she was the only person who believes he wasn't the one responsible, when other girls accused him.
Unknown to Haruna, Rito has harbored affections for her since he overheard that she was the only one who believed in him about the school garden incident before the start of the series, but because of his shyness and clumsiness, his numerous attempts to confess his love to her ended in failure. And unknown to Rito, Haruna has held affections for him as well. But she is hesitant to begin a romantic relationship with him due to her friendship with Lala, who is already pursuing a relationship with Rito.
Haruna also finds Rito to be very gentle, caring, compassionate and loyal. These feelings are furthered by the advice he gives to others, the way he treats plants and animals alike and how often he's willing to sacrifice himself for the sake of others. She has a romantic side to her with her feelings that long to be fully attached to him, even calling Yami "lucky" when they were accidentally attached together and unable to separate.
In Darkness chapter 54, Haruna's relationship with Rito takes an unexpected leap forward when the two are shrunken by Lala's invention and amidst trying to hide themselves, accidentally kissed each other. The next day, both are too flustered to face each other and don't know how to react to the accidental kiss with the one they harbored feelings for. But after pressure from Oshizu and Momo, both are on the verge of finally confessing to each other, but at the very last second, Haruna apologizes for the accidental kiss, and Rito simply forgives, leaving their romantic development back to nowhere.
Despite their somewhat implicitly intimate relationship, they still address each other by their last name (Haruna calls Rito "Yuuki-kun", and Rito calls her "Sairenji"). In Japanese culture, people who are close to each other often address their partners by their first name, and sometimes, they add honorifics (-kun, -chan, -san, etc) to determine their closeness. Judging by this, their relationship may not be stable and close as close friends; although they two are trying their best to overcome their shyness.
In chapter 75, she finally decides to confess her feelings to Rito after to Nemesis announces her plan to create a harem with all girls of Sainan. Haruna does not believe in a harem and that love should be monopolized. She gains the courage to confess when Rito screams a harem is impossible.
In chapter 76, Rito also admitted that he also has feelings for her . However, he refused to be in a relationship with Haruna because he also has strong feelings for Lala.
Haruna and Lala are best friends. It is because of her friendship with Lala that Haruna has been hesitant to pursue a romantic relationship with Rito. Lala, on the other hand, knows about Rito's feelings for Haruna, and is very enthusiastic to see them get together, believing that both girls can marry Rito together, as Japan's customs would no longer apply to Rito when he marries Lala and becomes King of Deviluke.
As of To love-Ru Darkness, she has learned that both she and Lala can marry Rito together, which greatly surprised her, realizing the reason for Lala's cheerfulness about Haruna's feelings for Rito. She currently doesn't quite know what to make of the newfound possibility.
Despite Haruna's huge fear of ghosts, she has become very comfortable around Oshizu, and the two have become good friends, and are often seen together. Oshizu is the first to learn of Haruna's crush on Rito after briefly possessing her, and becomes very supportive and encouraging towards Haruna confessing her feelings to him. She would even go as far as using powers to help, which usually fails in the end.
Haruna lives with her older sister instead with her parents who moved away. Occasionally she would tease Haruna about certain things like having friends over, which she greatly dislikes, but they do get along closely. She suspects that Haruna and Rito have romantic feelings for each other, and is "gleefully" supportive of them.
Risa and Mio are Haruna's close friends, and are often seen together in school. Haruna is less than amused by them constantly groping her.
Maron is the pet dog Haruna has at home. He is actually her older sister's pet, but because she is always working, Haruna is always the one taking care of him. Maron highly considers Haruna his master, and spends a great deal of time licking her, sometimes all over her body in a very perverted manner.