Ruri's rich and frail great-grandfather who lived in a huge Japanese mansion in the province. Yoshizou loved his great-granddaughter dearly, and like her, he wore a pair of circular eye-glasses. He constantly annoyed Ruri with his upbeat and perverted personality, which included collecting embarrassing photos of Ruri when she was a child. He considered Ruri as his own pride and joy, but worried about her life in the city, fearing that she may not have any friends because of her serious and deadpan personality. He later revealed to Ruri that his only dream before dying was to witness her marriage with the man she truly loves.
After hearing news that he may not have that much time to live, Ruri was forced to pay him a visit, and was even coerced to invite Raku to pretend as her boyfriend when the household mistook him as so. At first, Ruri thought that the apparent news was just another usual excuse her grandfather's been using again, to make her spend some time with him. When they arrived at Yoshizou's house, the old man became acquainted with Shū Maiko after the latter sold his rare photos of Ruri to him.
Like what she does with Shū, Ruri isn't shy about in hurting the old man in times when he shows his perverted nature. Still, the two has shown a very strong bond with each other during the visit, and Ruri even brought Yoshizou his favorite eclairs, as well as playing video games with him. However, a week after Ruri, Raku and Shū finally left the house, news came to them that Yoshizou died soon after, and a tearful Ruri regretted not smiling with him when he was still alive. In a very heartwarming scene, Shū dropped by to comfort her before she departs to Yoshizou's funeral; bringing with him a rare photo of Ruri smiling with his late great-grandfather during their visit.
Kosaki and Ruri have a strong relationship with each other. The two have been friends since middle school and have been stuck together ever since. Ruri is one of the only people to know Kosaki's crush on Raku and constantly tries to find ways to get the two together. Although Ruri knows the feelings between Raku and Kosaki, she is extremely conflicted by their denseness to realize their feelings for each other. Despite this, Ruri continues to encourage Kosaki's efforts to approach and confess her feelings for Raku.
Ruri is very observant of Kosaki; knowing details of her qualities, personality, and the way she acts, especially toward Raku. She deeply cares for Kosaki's well being and sees her as her best friend.
Chitoge and Ruri share a close bond with each other ever since Chitoge arrived to Japan. Like Kosaki, Ruri notices her traits - particularly her romantic interest for Raku - and considers her as a close friend. So much so that Ruri felt conflicted when she was rooting for Kosaki to confess to Raku. She is one of the few people to know the fake relationship between Raku and Chitoge.
Tsugumi and Ruri have a friendly relationship with each other. The two both share an annoyance against Shū and frequently beat him up when he makes a dumb/perverted comment. Ruri had seen Tsugumi as stiff at first but got to know her and learns she is actually a naive, embarrassing wreck due to her innocence.
Although the two aren't shown to be too close, Marika and Ruri are shown to have a mutual relationship with each other. Ruri says she has respect for Marika her single-mindedness and sees her as somewhat of a friend.
Overall, both Ruri and Shu consider each other as "glasses buddies" because of their obvious similarities in eyewear. Throughout the anime series, there are only a few instances where the two can be seen in romantic light, such as that time when Ruri was stoically annoyed when she learned that Shu received love chocolates on Valentine's Day. And there were also times in the manga when Ruri would show a defensive stance on Shu; such when she felt very anxious when a girl confessed her feelings to him, or when she beat him up after flirting with a bunch of girls.
Aside from that, Ruri once said that Shu somehow reminds her of her perverted late great-grandfather; whom she both loved and hated. As a tsundere, she would quickly dismiss any conversation about having a relationship with Shu, but even so, her friends admit that the two would turn out as a lovely a couple. Ruri had even dreamt of being married to Shu, much to her shock. She then shows the development of feelings for him, when she learns his future career as a teacher and his true kind nature but can never seem to dissuade the fact of Shu's nonchalant nature of showing his feelings towards other, dismissing his as someone whom she is uncomfortable to be with. After much contemplation however, and Shu's act of rescuing Rosa - a lost young foreign girl Shu and Ruri found - at the very last second, Ruri came to acknowledge that she is, indeed, in love with Shu, albeit considering him problematic. Eventually, Ruri came clean to Shu about her feelings for him after being enlightened by the struggles of confessing one's love, asking him to at least consider her as a lover after he had moved on from his feelings for Ms. Kyoko while feeling delighted seeing him dumbfounded.
In Chapter 229, it is shown that Ruri and Shu are probably living together and in a relationship, and they are preparing to get married in the future by starting to save money.
Both are good friends who show similar concern with Onodera. Although Ruri shows no interest in Raku, she is deeply annoyed with Raku's ignorance on Onodera's feelings. To the point that she almost spills the secret of Onodera's crush on him. Ruri is forced to ask Raku to pretend as her boyfriend to impress her grandfather she was planning to visit. Raku accepting Ruri's favor proves their friendly bond with each other.