The Niagato Family includes: Ari, Hirota, Cassandra (both deceased) and Miyana. When Ari was 13, her parents were killed in a car accident. She now lives under the guardianship of her older sister, Miyana who work hard to honor their parent's wishes.
Hirota was Ari's father, he was killed in a car accident along with her mother when she was 13 years old. Ari describes her father as passionate, driven and loving. She tells her parent's story whenever she gets a chance, and loves to talk about how amazing they were. Hirota had a strong passion for cooking which eventually drove him to open his restaurant, leading to their eventual wealth. He wanted nothing but the best for his family. One of his final wishes in his will was that Ari attend Ouran.
Cassandra was Ari's mother, she was described as beautiful, passionate and loving. She was born in America, but her parents moved her to Japan when she was in high school for her father's job. She loved Japan, and wanted to spend the rest of her life there. When she was in college she met Hirota, who was working as a waiter at a restaurant. Ari describes it as love at first sight, and it didn't take the two long to start dating. Cassandra loved her family, and always built their spirits high.
Miyana is Ari's older sister, caretaker and legal guardian. Despite being polar opposites, Miyana and Ari are incredibly close. Miyana is ten years older than Ari, and was 23 when they passed. They didn't have much family, so Miyana took legal guardianship over Ari after the accident. She is passionate about beauty and is currently attending school to be a cosmetologist, hoping to someday do hair and make-up for movie stars. She has a lot of know-how when it comes to being a girl and rich people, so she will often give Ari advice. Miyana is Ari's safe have, a place to go to whenever she needs help.
Ari has stated that due to Miyana's indifference and Ari's age, her father's restaurant chain is currently being ran by her uncle on her mother's side, as he was Hirota's best friend. Eventually, it will be passed down to his son, her cousin.
When Ari began school at Ouran, she was put into the same class as Kyoya and Tamaki. She didn't think much of the two until Tamaki approached her with an invite to the Host Club. She was incredibly unsure, but forced to try it out. She eventually got a hold of the situation and liked it, and was planning on joining the Host Club until Kyoya stopped her, telling her that he had preformed a background check and found out that she was a girl. He was hesitant to allow her into the group for fear of what would happen if the guests found out. Ari was upset by this, but didn't argue with him. When Kyoya realized that she had actually brought quite a few new guests (and by extension money) to the club, he invited her back in. She knew right away the reasoning behind his motives, but was fine with it. Due to Kyoya being the only one to originally know her secret she felt closer to him than the rest of the Club members. She found him interesting and wanted to know more about him, despite his seemingly apathetic nature towards her. As time went on, Kyoya did start to get a softer spot towards Ari, showing concern towards her on several occasions as well as sharing his ideas, and even plotting with her.
Ari was instantly drawn to Haruhi as there was now another girl in the club, but also knew that no one else knew so she kept her distance. She still enjoyed spending time with Haruhi, also finding they had other things in common. Haruhi was the first member of the Host Club after Kyoya to find out about Ari as she walked in on her changing after some punks pushed her into the fountain. Ari explained herself to Haruhi, and asked to keep her secret promising to tell the Host Club when she was ready, After this discovery, Ari and Haruhi were able to become closer friends. Haruhi defended Ari when she was found out and Tamaki threatened to kick her out of the Host Club. Ari has no romantic feelings to Haruhi, but has admitted attraction to her, this revealing her bisexuality.
Tamaki approached Ari with a proposal to join the Host Club, and Ari was instantly put off by his over-the-top personality and the fact that he was basically shoving her into a situation that made her incredibly uncomfortable. After joining the Host Club, however, Ari became more impressed with Tamaki's passion and drive. She began to admire him and even started looking up to him. When the rest of the club found out about Ari's true gender, Tamaki was the angriest. This sparked a huge fight between Ari and Tamaki and Ari accused Tamaki of not wanting to keep her around because she wasn't Haruhi. Tamaki threatened to kick her out of the Host Club so Ari told everyone to leave. After a long talk with her sister, she realized that Tamaki was upset because he had felt betrayed. Despite her fears, Ari built up the courage to talk to Tamaki in person and apologize for everything. Tamaki apologized as well as told her she could stay in the Host Club, he then saw it as a perfect opportunity for Haruhi to have a close female friend.
Ari's first impression of the twins was that they were jerks, reminding her too much of the bullies she faced in middle school. However, as she got to know them better she learned they were much kinder, though still incredibly loud and mischievous. As with most people, Ari saw Kaoru and Hikaru as the same person and it was impossible for her to tell them apart. Her perception changed once she spent time with just Kaoru, and learned that he was much more than he was when he was with Hikaru. She knew he still had a mischievous side, but there was a much kinder heart in him. After their time spent together, Ari and Kaoru spent increasingly more time together and Ari considers Kaoru one of her best friends, as does Kaoru.
Ari doesn't know Hikaru as well as she does Kaoru, but she knows that he is much more fiery than his younger twin. She wants to get to know Hikaru better, but doesn't know how to go about doing it. She knows he has feelings for Haruhi, and she worries how it will affect Kaoru. She admires Hikaru love for Kaoru, and often sees her sister in him. Hikaru has a somewhat of a protective nature of her rather than a romantic one. He knows that she is scared easily, and has quickly jumped to her defense multiple times.
Ari and Honey share a lot of common traits, but most noted is their passion for stuffed animals. Though Ari kept that side of her hidden for a while, when her gender is revealed she shares her collection with Honey and they share a profound love for the cute plushes. While sweets aren't her favorite, she loves to share cake and sweets with Honey. Despite his real age, Ari thinks of Honey as the younger sibling she never had. She always loves having fun and playing games with him.
Ari is often uncertain of what Mori is thinking, but admires him all the same. She takes great interest in his strength, bravery and dedication, often wishing she could have the same traits. Mori looks at Ari with a protective ideal. They have an unspoken relationship with shared respect and friendship.