Aria's opinions often clash with Kinji's, which is why she nicknames him "Stupid Kinji." Aria, however, is in love with him, but she doesn't show it due to her prideful nature. An example is when Kinji got sick, and Aria anonymously took the trouble to buy him medicine from a far location.Aria had initially fallen in love with Kinji not too long after they first met, but it was his Hysteria Mode that she found highly attractive. But later on in the series, it is constantly shown she actually harbors romantic feelings for Kinji and is too scared to confess to him. Instead, she keeps Kinji in a locked-relationship and doesn't allow Kinji to move in on other girls and vice-versa. Then, during the time period where Kinji had secretly transferred out of Butei High, it was shown that she really missed him and life was not the same without him. Also, after she rescued Kinji at the Kagataka Mansion, she was happy to see him again and was waiting for him when he came back to Butei High.
She can be very clingy and jealous if he even talks to other girls, especially Riko or Shirayuki. She became particularly jealous of Reki when she forcefully claimed Kinji as her husband and went as far as ending her friendship with Reki. Also, Aria jealous tendencies combined with her tsundere attitudes has caused her to unintentionally push Kinji away as shown in Volume 10, where despite Kinji having to make peace with Kaname, the girl who attacked her and the Baskerville girls, under orders from Deen, she saw him as a traitor and enemy until Volume 11, where she and the Baskerville girls got revenge and moved on like it did not happen. Then, in Volume 13 this continued, where despite being worried about Kinji after he missed his dinner with her, instead of showing signs that she was worried, she went to attack and berate Kinji. This caused him to lash back at her and leave to take on the mission by himself to her disbelief.
Via further insight, her relationship with Kinji is almost not unlike Holmes portrayed through the original novels towards his close friend John Watson and a few others, in that Aria tends to annoy Kinji because of her immature habits and causes him much irritation; though there are times Kinji and Aria trust each other more often as the series progresses, and as Kinji finds himself as the Watson to Aria's Holmes, more used to her absurd antics everyday, but working better with her at the same time regardless.
Initially their relationship got off to a rocky start after Riko, who misinterpreted why Aria had Kinji's belt, proposed the idea that Aria and Kinji were lovers to their class. As the series progressed, Aria's disdain for Riko only worsened when she learned that Riko was in-fact the Butei Killer. Despite learning of Riko's heritage and a rivalry that dates back to the 19th century, Aria isn't as concerned with defeating the descendant of Lupin as Riko is with beating the Holmes. However when Riko returns after being kicked out of IU Aria slowly begins putting more trust into Riko as she not only offered to testify for her mother but also help pin down Vlad. Eventually,she allows her to join Team Baskerville. Riko does love to tease Aria, often times flaunting her significantly larger bust and openness to get close to Kinji.
Aria considers Reki somewhat like a friend, even though the two don't necessarily socialize. This is due to both having similar traits: both being S-Rank and are short, petite girls. Aria also respects Reki, and it should be vice-versa. However, Aria may see Reki as an extremely powerful rival in the war over Kinji's affections, and the events shown in Volume 6 have shown that Aria was willing to break off their "friendship" over Reki's actions. After the events of Volume 7, the two now see each other as equal respectable rivals.
Aria and Shirayuki originally had a rough relationship due to Shirayuki's morbid obsession for Kinji. Aria would always have to keep her guard up in the event Shirayuki snaps assaults her. Following the Durandal case, however, their relationship progressively got better and Aria "recruited" Shirayuki into her team. However, Kinji suspected their relationship may not have been mere chance due to their connection to the Hihiiorkane (Scarlet Irokane).
Aria is Kanae's daughter, and Aria loves her very much, to the point where she'd be willing to put her life on the line to prove she's innocent. Also, like most mothers, Kanae has the capacity to embarrass Aria in a tight situation (Episode 4).
Aria is initially shown to dislike him/her for having a connection to Kinji to the point where she was willing to harshly antagonize him/her.
Aria seems to respect and idolize her ancestor to the degree that she compares herself to him and carefully preserves a picture of Sherlock in her belongings. When they finally meet aboard the IU, she seems mesmerized and unable or unwilling to act against him, even when Kinji's disapproval is clear. She ends up having to be 'rescued' from him by Kinji and her feelings toward him remain complicated.
Elle Watson is Aria's arranged "husband" setup by Aria's grandmother before they were both born. However, Aria showed no interest in the arranged marriage due to her love for Kinji and didn't seem to mind when the arranged marriage was called off following Elle defeat at the hands of Kinji. Beyond on this, Aria and Elle seem to be on good terms despite Elle drugging her to take her back to London, but does not know that Elle is a actually a girl.
Kaname and Aria initial relationship was very hostile due to Kaname having attacked her Shirayuki, Riko, and Reki causing them to be injured badly. It got even worst when Kaname essentially claimed Kinji as her and forced her out of his dorm room causing Aria to label Kinji a traitor and unknowingly caused her relationship with him to deconstruct. However, after Kaname was defeated in the lumberjack duel against Shirayuki and following the defeat of the GIII League, Aria apologized to Kaname and accepted her as Kinji's sister.
Aria and Kinzou (then GIII) relationship started off hostile as he was the one who ordered the attack on Team Baskerville causing her, Shirayuki, Riko, and Reki to be injured badly. After the GIII League was defeated, Aria relationship with KInzou is unknown due to their limited interaction with each other. However, they are willing to work together as shown when they saved Kinji, Moe, and Kikuyo from the Kagataka Family Syndicate.
Aria is jealous of Kinji's relationship with Moe as shown when she rescued her along with Kinji and Kikuyo at the Kagataka Mansion, and saw her hugging onto him and thinking she was his normal life girlfriend.
When Aria saved Kinji, Moe, and Kikuyo at the Kagataka Mansion, she was shown to be jealous of Kikuyo, especially when she saw her hugging onto Kinji.
Beretta was Aria friend while she attended Rome Butei High, but fought over who "owned" Kinji.