The Yuzuki household, oldest brother Hayato, second oldest Mikoto, second youngest Minato and the youngest Gakuto are having a family breakfast. Minato explains that their parents have passed away and the 4 brothers are maintaining the household together. Minato and Gakuto head off to school while the other brothers take care of household chores. Minato mentions that Mikoto and himself are close in age and in the same grade, due to being only 11 months apart in age. After a day in school, the next morning Minato tries to prepare breakfast but he ends up causing more work by burning what he prepared. Hayato scolds him and Minato is upset that Hayato treats him different from Mikoto despite the two being technically the same age. Minato notices that Gakuto wants to see the fireworks at a festival so he resolves to take him there himself, hoping that Hayato will treat him as being mature if he can do this. Minato and Gakuto have a fun time, however Minato loses Gakuto and has to search for him. He can't find Gakuto, but Hayato and Mikoto show up and manage to find him, Hayato goes easy on Minato since he understood his brother had good intentions. They enjoy watching the fireworks together as a family.

Mikoto brings Minato his lunch, Minato's friend remarks that Minato doesn't call Mikoto his older brother. Mikoto has a flashback showing that he did not like Minato much during his childhood, as Minato was born premature and received far more attention than him, but Mikoto grew fond of Minato over time.

Gakuto talks about how he wants he wants to also contribute to the household like Minato or Mikoto are now doing. In a flashback its shown how the Yuzuki family got in contact with the Kirishima family when their parents passed on. During the flashback its revealed the extended asked Hayato to least send Gakuto to other relatives given how young he is, but Hayato absolutely refused and decided to raise Gakuto regardless how hard it would be. One day while waiting for his family to come home, Gakuto is invited into the Kirishima household and has apple juice, he notices that the head of the household, Kojiro, treats him in a very mature way, introducing himself and asking him what he wanted to watch. After Hayato comes home, Gakuto tells him that he would like to go to the Kirishima household more often after school and says he likes going there. Hayato agrees to this and asks Kojiro if he can impose by having Gakuto come over after class every day as it would also make his teaching internship go easier, Kojiro is delighted and says he would love to.

Hayato goes to a highschool reunion, he meets a lot of his former highschool classmates and remarks on how mature they look and how relentless the passage of time is. Three girls approach Hayato and flirt with him now that they see he has a stable job and still looks handsome. Hayato reveals that he is taking care of his three little brothers to everyone's shock, he explains that he blows away most of his money on them but he enjoys taking care of his family. After the conversation ends, he overhears the three girls talking behind his back on how old man like he is and how they lost all interest in him, which upsets him. Walking home from the reunion he runs into Saki Kirishima whose on the job as a police officer, she says she's about to finish her shift and asks him to have a drink with her. They discuss what happened at the reunion and she tells him that he should be proud of how well he's raising his family and cheers him up. After he goes home, his brothers surprise him with a birthday party, Hayato had forgotten that it was his birthday and very excited to celebrate with his brothers.

A boy approaches Uta and confesses his love to her, she accepts but does not really understand what that entails. Minato's friends note that Minato treats Uta more like another male than someone of the opposite sex. Minato is excited for Uta and happy she got a date, he points out that's amazing and that Uta is like a real adult and one step ahead of him. They hold a strategy meeting to decide what Uta will wear for the date, however they can't decide what she should wear, Gakuto recommends they ask Hayato for advice. After talking to Hayato, Minato decides on what Uta will wear. Minato realizes now that Uta has a boyfriend, they might not be able to talk as much, he feels upset at the thought and then also happens to catch a cold. After getting over his cold, Minato enlists the help of his brother and friend to break Uta up from her new boyfriend so she spends all her time with him instead. After discussing with his friends, they suggest this approach isn't a good idea and that maybe he should try to date Uta instead.

The three boys discuss the situation further, Minato decides that him dating Uta is out of the picture and that he doesn't want that sort of relationship with her. The next day Minato tries to spend some time with Uta, but she wasn't willing to hang out with him. He tries to get closer to her again but is unable to, and he learns from Uta's mom that she probably is not in love and there might be another reason why she seems withdrawn. He eventually meets Uta near their fort, she explains to him that the boy she dated said her behavior was very masculine and unfitting, that she should just act like a girl, which hurt her and Minato realizes this is why she hasn't been herself lately. He tells her that she should just be herself and to ignore someone who doesn't really like her for who she really is. Uta takes his advice and cries happily to Minato, saying that he really is her best friend, and she breaks up with the boy, who she wasn't a good fit for.

While building their fort, Mikoto talks about how Minato first met Uta. The Yuzuki family met the Kirishima family shortly after their parents died. At first Uta does not get along with Minato at all, turning down all his attempts to befriend her and generally being very difficult to be around. It's explained that Uta's parents were separated and Uta was blaming her mom for the break up. Minato overhears Saki talking to Hayato on Uta blaming her for the breakup and runs out to confront her. After having a fight, Minato tells Uta she should talk with her mother and should be grateful she has a mother in life. Minato and Uta discuss Minato’s reasons for being an uplifting person despite his parents passing away. After hearing him out, they come back home bruised and Uta asks her mom why she got divorced, her mom explains that Uta's dad was cheating on her. Uta recalls times when she traveled with her father to multiple restaurants with his many female companions. Upset that she knew, her mom punishes Uta with a joint lock. Uta asks Minato to become close friends with her and he accepts. In the present, Mikoto reveals those two have been best buddies since that time. However, he argues that their relationship will never be on par with his companionship with Minato.

Gakuto is keeping a secret from his family, due to this he seems a bit strange to the rest of them in terms of his behavior. Gakuto is hiding a visitation form from his school because he wants to be considerate to Hayato, who will most likely take a day off from work to visit. He tells Waka his secret and Waka says they won't show their mom the form either, because their mom might tell Hayato as well. The head of the Kirishima household hears this plan, and proposes to the kids that he go as Waka's grandfather and Gakuto's family friend instead. Gakuto tries his best to keep the secret, but Minato already overheard the conversation, so he is also behaving strangely at dinner. Minato decides its in Gakuto's best interests that some who is family visits the school, so he goes to grab the form from Gakuto's backpack.

Minato tells Uta that he is going to skip school the next day so he can visit Gakuto during the visitation day and asks her to cover for him, which she agrees to. When he is about to leave for the school, Mikoto catches him and asks if he can come along after he realizes the situation. With both of the boys gone, the teachers let Hayato know, and Hayato realizes that he needs to visit Gakuto as well, which leads to the entire family showing up. Gakuto is shocked when he sees this, he reads out loud in class to try and impress his brothers. When they finally get home, Gakuto starts crying because of how many people he caused trouble for hiding his secret, including Uta, who got scolded by the teachers for covering for Minato skipping school, but everyone assures him that it's okay for him to rely on his older brothers more and they are happy to have been there.

Mikoto's daily school life is shown and it is noted he's admired by most of the school body, also that he has a strong sense of love for his younger brother Minato. There is a flashback to when their mother was in the process of giving birth to Gakuto and Minato starts crying because he wanted to see his mother, however Mikoto calms him down. The brothers discuss their soon to be born new brother and Minato asks Mikoto what having a little brother is like, Minato praises brotherhood and says its the greatest thing. Gakuto is born and Minato is afraid to touch him, but with some encouragement from Mikoto, he eventually does and he grows really close to Gakuto after. Minato spends time feeding Gakuto and playing with him, they form a good relationship. Mikoto feels a little left out now that he longer has the full attention of his little brother, but he accepts it having two adorable little brothers.

Uta's family is going on a hotsprings trip, the brothers tell Hayato that the Kirishima family is going on a short vacation. Hayato starts sneezing and slowly shows signs that he has a cold, the next morning breakfast is not ready because Hayato is ill. The brothers make him breakfast and help take care of the household chores, Minato takes Hayato to the hospital. The brothers go shopping and get dinner, Hayato's fever gets better at first but then gets worse, he eventually throws up. Eventually Minato realizes the fever has reached a dangerous threshold, so he calls Saki and asks her for help, she leaves the kids with the Kirishima family head while driving Hayato to a hospital. While eating dinner at the Kirishima residence, Minato apologizes for disturbing their family while they were on a trip, but they say its no big deal and he was right to call for help. Hayato recovers from his cold after 5 days and is ok, Saki and Mikoto however catch his cold, but its indicated they will be fine as well.

Gakuto begins writing in his diary, recording his daily life and notable events, he also explains and analyzes what he has learned each day. He goes around asking his brothers what they think of him and how they feel about their other siblings, he learns some interesting things about how they see him. The brothers go out, due to the rain they dress up in coats and boots, they head to the graveyard to leave flowers at their parent's graves. While on the way there, Gakuto remembers his parents and when leaving the flowers he feels sad at their passing, the rain ends and Minato points out a rainbow which uplifts Gakuto's spirits. The brothers extend their outing and have a picnic together, then head home and Gakuto adds the way to his diary as another pleasant day.