Ruri is short in stature, has long purple hair with a piece of hair sticking out from her head and has yellow eyes. She is usually seen wearing a long sleeved white and lavender frilled shirt, along with an orange scarf and a short red skirt with black over the knee socks.
At a young age, Ruri was abandoned by her parents at an unknown desert and was later saved by Dolly who took her in and raised her as her own daughter. Years later, after being trained in systema, Ruri is sent to Japan to acquire the Kurotsubaki for her adoptive mother Dolly, Which was believed to be within the Sanzenin mansion.
Ruri first appears after overhearing Hayate's conversation with Nagi, after calling him by his full name and asking him if she is a friend? or an enemy? before introducing herself to him as "Princess Tsubaki", ignoring what she said, Hayate mistakes her for a lost little girl, much to her annoyance. Warning him that danger is behind him, Nagi is thrown into a car and kidnapped by a couple of masked men. While planning to herself that this is the part where she comes in and saves Nagi and takes the treasure as her reward, Ruri suggests reasons to Hayate on why Nagi was kidnapped, not paying attention to her, Hayate commandeers Ruri's bicycle against her wishes and ends up taking her along with him while in pursuit of Nagi's kidnappers. After saving Nagi and feeling humiliated from what happend, Ruri vows to Hayate that he'd pay for what he has done, before leaving. Later she reappears before Hayate and Maria at The Sanzenin mansion introducing herself as Nagi's little sister.
After Ruri's revalation that she is Nagi's little sister, Hayate and Maria go back inside and slam the door shut without listening to Ruri. The next morning to her surprise, Nagi opens the door and finds Ruri sitting outside at the same place from the previous night, Shivering from being outside all night and trying to speak to her, Nagi ignores what Ruri is trying to say and slams the door on her again. Later after seeing Maria returning from shopping, Ruri grabs onto her leg and begs for her to listen to her story. After being let into the mansion by Maria and explaining to Nagi on her claim that they are related, Nagi begins question her agenda and asks what she wants by visiting her, after revealing to Nagi that she has never met her father and that her mother is dead and that she has no other relatives and has only heard about Nagi and located her out of love in order to meet her. Upon hearing her answer Nagi allows her to stay at the mansion then asks her to wait in the hall till she sort things out. While waiting in the hall, Ruri begins to search for the treasure that she mentioned to herself earlier and begins searching inside a vase and is caught by Nagi who realizes her true agenda and then arranges for her to live at The Violet Mansion
After taking Ruri to the Violet Mansion then introducing her as a new tenant to Chiharu, Ayumu and Kayura. Ruri objects on staying there and tries get Nagi to give her another chance, still being ignored by her, Ruri addresses her as Onee-chan (older sister) in order to gain her attention, taken back from what she just called her and then listening to Kayura suggestion, Nagi decides to give Ruri another chance to prove herself by demonstrating a special skill, Ruri reveals to them that she is a master of systema then demonstrates her skill by beating up Hayate as revenge for what he did earlier, After taking the fight outside, Hayate counters her attack with ketaguri and defeats her, After sitting up and crying from what he did, Hayate apologizes and tries comfort her, but turns out to be nothing more than a ruse by her and attacks him once again before receiving a kick to the back of her head by Nagi for what she did. Nagi tells Ruri that she has no place to call her Onee-chan (older sister) but will allow her to stay at the Violet Mansion then (along with Chiharu and Kayura) compliment Ruri's skills in systema asking her to teach them.
Later, early in the morning at the Violet Mansion, Ruri reports to a mysterious blue bird, revealing that her true agenda is to aquire the Kurotsubaki which is believed to be at the Sanzenin Mansion. wanting to get closer to Nagi, so she could get a chance to gain access to the mansion. Ruri goes to Nagi's friends, Chiharu and Kayura to learn more about her intrests. after taking both their advice and spending 34,150 yen on video games that Nagi might like, Ruri meets Hayate who informs her that Nagi already owns the video games that Ruri just bought and thought that they sucked. after overhearing such news Chiharu and Kayura demands Hayate to bring Nagi to them, after coming back with her and then witnessing an arguement between the three otakus, Nagi takes Ruri to Akihabara to teach her about games and anime, after visiting many places and getting tired of listening to Nagi, Chiharu and Kayura argue, Ruri finds a Doujinshi at Wataru's shop that she likes and buys which Hayate reconizes as the same doujinshi that Nagi sold at Comiket.
Later, wanting to visit Chiharu and Kayura, Nagi finds Ruri alone at the Violet Mansion. Not having any business with her, Nagi tries to leave but is unable to due to the sudden a rain storm, with no choice but to stay there for the time being, Nagi asks Ruri to talk about herself, asking her once again what her agenda is, Nagi then tells her that if she was honest with her, she'd might be able to help her. refusing to reveal her true agenda to her, Nagi pulls out a fish sausage which she bought earlier and begins to eat it, noticing that it has caught her interest, Nagi tells her that its foie gras and offers to give it her only if she told her what her true agenda is, unable to resist the temptation, Ruri reveals to her that her true agenda is to obtain the elusive Kurotsubaki, a treasure believed to be in possession of the Sanzenin family. Unsure what it is, Nagi calls Mikado, who reveals to them that the Kurotsubaki was stolen 13 years ago then refuses to tell them who the thief was causing Nagi to smash her phone. As the storm outside worsens the mansion starts to shake and the ceilings begin to leak, the both of them struggle to keep the mansion in one piece, while trying to close the doors Ruri asks Nagi to check on the leaking roof and everyone’s room, As Nagi runs along the corridor a tree branch outside flies towards her, Ruri saves Nagi from being hit by the large branch at the last moment. After the storm passes, Hayate arrives to check on them, Nagi asks Ruri why she saved her as there was no longer a reason for her to get close to her anymore. Ruri tells her that she doesn’t help people for a reason before being interupted by Hayate who gets a call from Mikado who reveals to them that the person who stole the Kurotsubaki was Shin Hayek.
After learning from Nagi that the Kurotsubaki is among Shin's belongings in Las Vegas, Ruri tries to persuade her to go there, but Nagi refuses to go then reminds Ruri that she doesn't have the money to buy a plane ticket to go there herself. The following day, Desperate in finding a way to go to Las Vegas, Ruri sees a flyer for a quiz contest at a fair, where the winners will get two plane tickets to America. Seeing her opportunity, Ruri decides to enter Nagi and herself in the quiz contest hosted by Fumi. Before signing up for the contest, Nagi explains to Ruri that the Kurotsubaki is a clock that'll bring bad luck owner and advises for her not to go after it.
After losing the contest, Ruri runs into a nearby forest, thinking about what Nagi said before running into the myserious blue bird from earlier, Who reminds her what her purpose is to acquire the Kurotsubaki and asks Ruri if she had any leads, After telling the blue bird that she doesn't have any leads, Isumi attacks the bird (revealing that it was made of wood) and asks Ruri who she is and why she's trying to get close to Nagi, before Ruri can say anything to her, Shidou intervenes, fed up with how Ruri has been handling things, he tells her that that if Nagi has to go to Las Vegas to get the Kurotsubaki then its her job to get her there before grabbing her, before he could make his escape he is stopped by Isumi, Hayate and Hinagiku. After rescuing Ruri, Hayate asks her who Shidou was, refusing to tell him, Ruri then asks him if her big sister would be worried about her if she was kidnapped, telling her that Nagi would be worried, smiling from what he said, Ruri heads back alone.
While on her way back, Shidou appears behind Ruri, then asks her why she lied about the wheareabouts of the Kurotsubaki then suggets for her to abduct Nagi in order to acquire it, Ruri tells him that she won't let him endanger her sister, Shidou then asks her if she intends to betray her mother, telling him that she won't betray her, Ruri tells him that she has a way to solve everything peacefully, then asks him to loan her some money for a plane ticket much to his chagrin.
After sending a fraudulent ransom note to Nagi, Ruri later appears after being summoned by Dolly, she is then ordered to locate the Kurotsubaki, after Nagi failed to bring it as requested in the ransom note. Locating the Kurotsubaki among a bunch of thieves who are trying to make their escape with Yukiji's money, Ruri takes out a majority of the thieves with her skills in systema, then aims to grab the Kurotsubaki from one of the thieves, however the thief activates the Kurotsubaki, causing it transform into a sword. Ruri is nearly stabbed in the process before Hayate throws her out of the way and is impaled by the sword himself. After witnessing Hayate miraculously "survive", Dolly makes her move and appears before "Hayate" demanding the Kurotsubaki for Nagi's safe return, but is cut short after Isumi attacks Dolly causing Ruri to attack her in anger, giving Shidou enough time to retreat with Dolly before retreating herself.
Ruri later appears behind Nagi and grabs the Kurotsubaki from her before succumbing to its bad luck after a few Halloween decorations fell on top of her, Nagi then requests Ruri's help by bringing Dolly's ring to her, as Hayate's life depends on it. Agreeing to bring it, Ruri later attempts to take the ring while Dolly is bathing, but is caught in the act, after Nagi sent her a text message to meet her at the Starside hotel. Arriving to the place of meeting, Dolly throws Ruri into the wedding hall before attacking Nagi and Shin. Ruri pleas to Dolly not to push herself any further, which angers Dolly even further causing her to attack Ruri, before destroying the wedding hall. Afterwards, Ruri saves Shidou from being harmed even further by Isumi's attacks, She then asks him to take Dolly back to the sanctuary, before trying to hold Isumi back. While confronting Isumi, Ruri reveals to her that she was saved by Dolly after her parents abandoned her in a desert, after being hit with one of Ruri's kicks, Isumi decides to no longer hold back and unleashes a powerful attack knocking Ruri unconscious. After being tended to by some paramedics, Ruri is later seen mourning Dolly's death while holding Shin's wedding ring, afterwards Ruri is last seen returning Shin's wedding ring to Nagi before departing with Shidou.