Fuutarou Uesugi/Relationships

Fuutarou prefers solitude, in which his friends remark that Fuutarou is "by himself again." and Yotsuba said that Fuutarou is seldom to be sociable.

Fuutarou's type of girl is "full of energy", "good at cooking" and "cares about her brother" (but he is actually referring to Raiha Uesugi).

Isanari Uesugi
Isanari is Fuutarou's father. Fuutarou used to be quite similar to the kind of person Isanari is now, a boisterous and 'wild' man. The two of them share a good relationship with each other as father and son, as they can joke around with each other casually. Isanari is shown to care a lot for his son's well-being, demonstrated by encouraging Fuutarou to go on the field trip and enjoy himself and he is not above trying to discipline his son, albeit not succesfully.

Raiha Uesugi
Raiha is Fuutarou's younger sister. Fuutarou cares dearly for his sister and does his best to try and fulfill all her wishes. He is also rather protective of her, as shown by when he rushes to her side when she's sick and willing to abandon his long-awaited school trip to take care of her. Raiha also cares for her older brother a great deal, although she is not afraid to criticise him and correct his behaviour whenever he acts rude, specifically around the quints. As a part of taking care of her brother, Raiha also cuts Fuutarou's hair.

The Nakano Quintuplets
Fuutarou refers to the day he met the Nakano Quintuplets as a nightmare. Fuutarou's goal is to make the sisters graduate without problems. Fuutarou has a book called "The Quintuplets Graduation Plan", one of the content is the detail of Nakano Quintuplets' mock test results. Early on the series, Fuutarou comments that dealing with all five sisters is hard. Itsuki says as long as Fuutarou has love, he will be able to identify the sisters. As time passes, Fuutarou changes as a person by spending time around the quintuplets, becoming aware that there are more things to the life of a student than just studying and he eventually grows to love them all like family and takes pride in having been their tutor.

Ichika Nakano
Ichika calls Fuutarou "Fuutarou-kun." Ichika's first impression of Fuutarou is that "he's a bookworm who doesn't have a girlfriend." Fuutarou's first impressions of Ichika is that she has "eyes that seem to see right through you." They have both shown to be rather perceptive of each other, such as when Fuutarou was able to detect her fake smile and when Ichika is able to tell how Fuutarou acts weird sometimes.

Ichika initially had a pessimistic view towards the sisters' capability to study, making her reluctant to be tutored by him. Her attitude lasted for quite some time until he helps Ichika to overcome her problems and made her closer to the sisters. Ichika likes to tease Fuutarou, but he is rarely flustered by it ; Ichika actually finds herself flustered by his actions now and then

Over time, Ichika ends up falling in love with Fuutarou because of the little things that he notices about her and remembers  but is reluctant to act on her feelings due to her awareness of Miku's feelings for him. She is further discouraged by Nino's bold confession to him but after Yotsuba encourages her to do what she wants, she takes the wrong approach to winning over Fuutarou's love, using lies and deception and betraying Miku , despite having supported her sister's feelings initially. Eventually, Fuutarou himself calls her out harshly on her lies, although he then feels remorse over his actions and apologises to her.

WARNING: MAJOR SPOILERS AHEAD

Nino Nakano
Nino's first impression of Fuutarou is "someone persistent and not popular." Fuutarou's first impressions of Nino is someone who is self-righteous.

Nino labels Fuutarou as "dull-looking guy." Yotsuba notices that Nino doesn't directly kick Fuutarou out of the house after the midterm exam. Nino is antagonistic and openly rebels against Fuutarou since their first meeting. She is seen boycotting Fuutarou's attempt to tutor the quints in several occasions. Fuutarou notices that Nino is someone who "scheme."

Over time, due to Fuutarou noticing Nino's other side as a caring sister, she began to accept him. After knowing her sisters' acceptance to Fuutarou, she defends Fuutarou against her father. Nino is the only sister who rarely calls Fuutarou by his first or last name, using "you", "that guy", or other third-person nicknames. Despite the harsh treatment he gets from her, Fuutarou cares her just as much as the others and is always ready to help her when she's in trouble, even willing to "call" Kintaro, knowing that Nino wanted to see him.

Fuutarou tells Nino about Rena, their past, and the day's encounter with her to Nino after she brings him to her hotel. Through her interactions with "Kintaro" and later Fuutarou as himself when they were alone, she realizes the reason for her hostility was that she was rejecting him due to his status as a mentor, not for his character or him "disrupting their family."

After Nino had initially confessed to Fuutaro, she often tries to get close to him as much as she can, including taking the same part timer job after the Nakano quintuplets decided to no longer live with their father's guide. She confesses to him again since he did not hear her the first time and admits that while she has not given him a reason to return her feelings so far, she would make him notice her. Since then, Nino has become much more flirtatious and direct with her feelings. She now refers to him as "Fuu-kun", much to Miku's displeasure.

Miku Nakano
Miku calls Fuutarou "Fuutarou." Fuutarou's first impressions of Miku is that she is someone you can't get a read on.

Miku initially rejects Fuutarou as a tutor because she's expecting someone better. After Fuutarou found out about her secret interest in warlords, and appreciated it, Miku began to accept him, only to reject him again due to Fuutarou's lack of knowledge. He spent a lot of effort in convincing her again, and successfully get her approval. Fuutarou also motivate and inspire Miku to start studying, making her the second sister who accepts Fuutarou as a tutor.

Due to Ichika's actions, Fuutarou almost doesn't think Miku holds romantic feelings for him and believes Miku supports the idea of him hooking up with Ichika. But he wants to ask what's the meaning of Ichika's whom he believes to be Miku's action on her because Fuutarou still feel vague about it.

Fuutarou later realizes and admits to Yotsuba that Miku does have feelings for him. In Kyoto, Miku gives Fuutarou some bread and is the first girl who Fuutarou talks about his mother to. When Miku confesses to him by pointing to things she likes around them before pointing at him, he smiles and replies with "I know." Before he can say anything further, Miku diverts his attention that she also likes her sisters, who were behind him watching the whole time. She playfully teases him about what she could have meant by saying she likes him, confusing him and causing him to say that you "don't mess with a guy like that". Despite Fuutarou's confusion, Miku is confident he knows what she meant. During the school festival, she asks Fuutarou to a date, in which she tell him that instead of university, she will go to culinary school. Right after, she says that he is special to her "in a weird way," finally giving a direct confession.

Yotsuba Nakano
Yotsuba calls Fuutarou "Uesugi-san." Her first impression of Fuutarou is "someone gloomy and doesn't have many friends" and Fuutarou's first impressions of Yotsuba is that she is a simpleton.

Yotsuba is the only sister who accepts Fuutarou as a tutor from the very beginning. This was likely due to knowing and remembering him from the Kyoto trip five year before. She happily cooperates with him to help make her sisters accept him as a tutor. As they spend more time together, Fuutarou slowly changes and learns to appreciate other aspects of life, such as having fun which is shown during the test of courage during the field trip, when he and Yotsuba scare people together and he even writes about his experiences with Yotsuba and her sisters in a diary, such as learning skiing from the former.

Fuutarou and Yotsuba end up going on a date together during Labour Thanksgiving Day, primarily because Raiha guilt-tripped her brother into getting a gift for Yotsuba to repay her for her help during the field trip. After going to four different places during the date representing the other four sisters, Fuutarou finds himself enjoying the date for the first time when he and Yotsuba go to her favourite place - the park - and the only time he is shown laughing in joy is when they play on the swings together. Fuutarou is also shown to be more physically comfortable with Yotsuba than the other quintuplets, as he frequently grabs her ribbon when berating her and fixes them right after; other instances of the two being touchy-feely include the time when Fuutarou was not afraid to cover her mouth with his hand to prevent her from being heard by the track team captain Eba and when he grabs her by the shoulders in the ferris wheel when he gets an idea about improving the quints' studying habits. He learns of some of her past issues and is determined to help her out to overcome her problems with studying.

After the third year of high-school begins, Yotsuba nominates Fuutarou to be the class representative to get people to understand how great of a person Fuutarou is. She additionally declares that whoever Fuutarou grows to love, she will support him in that love.

WARNING: MAJOR SPOILERS AHEAD

Itsuki Nakano
Itsuki is the first of the quintuplets that Fuutarou meets and quickly had a quarrel with, leading her to reject him as the sisters' tutor early on. Due to Fuutarou's consistent efforts, Itsuki began to notice the change on her and the sisters. Itsuki usually compares her father to Fuutarou due to her mother's words. She and Fuutarou develop each other's character, as they both overcome their stubbornness. 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. During the Scrambled Eggs Arc, Itsuki is revealed to feel that their relationship is no longer that of partners, but to that of friends. When Fuutarou accepted this, she was overjoyed and quickly ran to the mixed bath he was in to join him, being embarrassed when she realized what she was doing.

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.

WARNING: MAJOR SPOILERS AHEAD

Rena
Fuutarou consider his feelings toward Rena as admiration and gratitude, something Nino thinks is instead love. While he didn't want Rena to see him and attempted to run away, he later spends time to talk with her. Following his realization that Rena was one of the quints, he tells her that he is annoyed at the sisters' usage of disguises to get closer to him. When Rena asks if he knows which of the quints she is, Fuutarou states that he doesn't care all too much, something she interprets as him not caring about her anymore.

Takeda Yuusuke
At first Fuutarou was put off by Takeda talking to him in the school bathrooms. Takeda saw Fuutarou as his rival, despite Fuutarou not knowing who he is. Later they become enemies during the National Mock Exam arc as Takeda tries to take Fuutarou's job as tutor and Fuutarou responds by announcing that he will place in the Top 10 nationally.

Takeda eventually earns Fuutarou's respect and recognition as a rival when he refuses to cheat in the exams, and then talks of his dream to become an astronaut. After the arc they have formed a friendly relationship, and they form a group alongside Maeda in for the Kyoto school trip.