Itsuki Nakano/Relationships

Itsuki doesn't like her sisters quarrel with each other, and being the "youngest", she can get easily intimidated by them.

Maruo Nakano
Maruo Nakano is the adoptive father of Itsuki and her sisters. He describes Itsuki as someone obedient and sensible. Maruo Nakano He also contacts Fuutarou through Itsuki.

Mama Nakano passed away on August 14, and Itsuki visits her grave every month. Nino said Itsuki does it because she's conscientious, but Fuutarou doubts it.

Ichika Nakano
Ichika calls Itsuki "Itsuki-chan." According to Fuutarou, Ichika is the only one who address Itsuki as "Itsuki-chan." Itsuki notes that Ichika have been forcing herself because of them.

Ichika mostly showed her big sister attitude towards Itsuki, expressing care and protective behavior. Ichika noted that Itsuki hasn't been able to be honest with herself. Ichika stated that Itsuki and Fuutarou fight all the time because both are similar, a stubborn person.

Nino Nakano
Nino is the one who usually wakes up Itsuki. Nino pairs with Itsuki, for the Test of Courage.

Itsuki is the closest with Nino, as both are seen doing activities together, such as shopping, lunch, and test of courage. Nino is also very protective towards Itsuki, being the most vocal sister regarding her well being. The two come into conflict shortly before the final exam of their second school year, with Itsuki uncharacteristically slapping Nino for insulting Fuutarou and throwing aside her copy of the handwritten notebook he made for them. The two of them then leave the Quintuplets' apartment for a week, with Nino going to a hotel and Itsuki staying with the Uesugis. The two eventually rekindle, with both of them having bought movie tickets to watch together.

Miku Nakano
Itsuki is aware of Miku's fondness towards Fuutarou, and she reassures Miku about his circumstances, showing her care to Miku.

Yotsuba Nakano
Itsuki consoles Yotsuba by showing her Fuutarou's notes praising Yotsuba. Itsuki is the first to learn of Yotsuba's past with Fuutarou, and is asked to disguise herself as Yotsuba from 5 years ago. While Itsuki believes that Yotsuba deserves a chance with Fuutarou, Yotsuba refutes it, feeling undeserving of it and wanting to not be the only one who is "special" to him.

Fuutarou Uesugi
Early on, Itsuki had a quarrel with Fuutarou, leading her to reject him as the sisters' tutor early on. Despite this, she took him home after his disastrous first meeting with the sisters and begrudgingly encouraged him to try again after having dinner with the Uesugi family. She refused to consider the two of them as anything but strangers at first, partly due to Fuutarou's mutual sentiments. Due to Fuutarou's consistent efforts, Itsuki began to notice the change on her and the sisters. After having a number of arguments with Fuutarou, she wants to apologize but feels too awkward to do so until being encouraged by Ichika to be honest with herself and the reason they argue is because of how similarly stubborn they are. She and Fuutarou develop each other's character, as they both overcome their stubbornness.

Itsuki usually is the one who compares her father to Fuutarou due to the words of her mother who says to be cautious when choosing men. Despite their initial tensions, Itsuki is disturbed by the condition placed on Fuutarou by her father, and at first refused to disclose her first test scores, knowing that Fuutarou would be fired. She held reservations towards Fuutarou for both his role as a tutor and as a potential romantic interest for the sisters before the school trip and wished to use the trip to prove his character. During the trip and after finding his written notes of stories to tell Raiha when he goes back home, she realizes that she did not know Fuutarou at all and tells an unconscious Fuutarou of her desire to learn more about him. When Fuutarou is hospitalized after the trip, she visits Fuutarou to do just that, and spontaneously asks about his motivation for studying. During the Scrambled Eggs Arc, she considers her relationship with him as that of friends rather than partners. When Fuutarou accepted this, she was overjoyed and quickly ran to the mixed bath he was in to join him, before being embarrassed. Eventually, it's implied she may have feelings for him; she's grouped within the same category as Nino and Ichika, wanting to walk around and explore with him alone.

She knows more regarding Fuutarou than her sisters, being aware of his family's financial situation and is the first one he disclosed part of his past to. When Itsuki has a fallout with Nino due to Nino rejecting Fuutarou's efforts, she stays at Fuutarou's apartment due to her sisters not knowing where it is and she had nowhere else to go.

Itsuki says that it's unusual for her to warm up to someone like Fuutarou. She often notices when he acts unusual, such as asking the sisters to use the same hairstyle and realized he was doing that because the girl he had met was one of them, or when he was acting distant following his reinstatement as the sisters' tutor following the mock exam. She was overjoyed by the news and was annoyed by Fuutarou's lack of response, not knowing that he had just been reminded by her father to act properly towards the sisters. She sensed that something was bothering him and was eager to learn about it.

During the ending scene of Quintessential Quintuplets 2, a scene is shown where Itsuki ran up to Fuutarou, falling on him and kissing him under a bell.

Raiha Uesugi
Itsuki is the 1st quint to meet Raiha. Itsuki develops a fondness toward Raiha due to her cuteness and partly after learning Uesugi family's circumstances. Initially, Itsuki only exchanged her contact information with Fuutarou in return for Raiha's. The two would even hang out with each other during the school holidays. It is implied she contacted Raiha following her fallout with Nino to stay over at the Uesugi residence for a while.