He is the grandfather of Makabe. For the eight years that Makabe was fat, his grandpa had trained him by making him exercise and cut down on eating junk food. Makabe appreciated it but also felt that his grandpa was being harsh on him.
Makabe is the son of Kinue. Their last names are different because Makabe decided to take his grandfather's last name. Kinue loves her son a lot and Makabe shares the same affection despite his mother giving him food with too many fat and calories, which irritates him.
Chinatsu is the younger sister of Makabe. She teases her brother, by calling him a 'lolicon' and such due to his strange interest in shoujo mangas and having a picture of Aki and him when they were younger.
Masamune and Aki are childhood friends. He first met her by accident because he was running away from some bullies and when he realized he was inside Adagaki property. From that point they would hang out together in her garden. It is shown that he was in love with her and the feelings were mutual as she was also in love with him. When he confesses his love, for unknown reasons she rejects him telling him that she can't come to like someone like him, later giving him the nickname 'Pig's Foot'. This is the main reason that triggered him to train his body and become thin and handsome.
After growing up, he first transfers to her school only to take revenge on Aki. His plan involves making her fall in love with him and mercilessly, the same brutal and humiliating way Aki does it, reject her. Later he teams up with Yoshino (Aki's maid) to humiliate Aki who'd reject any confession and along with that, give the rejected a nickname. It is unknown what his true feelings are but it is true that he feels the most irritated when he sees her with her fiancee.
In chapter 34, Aki tells him that she cannot accept Masamune's feelings while telling him about the Masamune she met in her childhood and loves. She also tells him that when she told Masamune about her parents splitting up, she started crying, in which childhood Masamune says that he will always be with her, but after that, Masamune disappeared and never came back until now. She also tells him that Masamune's disappearance resulted in her habit of binge eating and now that he has come back, (Kanetsugu Gasou) he still doesn't feel any guilt for leaving her behind without saying a word. This leaves Masamune in confusion as he thinks what Aki is saying is different from what he has in his memory.
But he soon snaps at her and his hatred reached to a point where he couldn't hold it in. He recalls all the events that occurred in his childhood and the fact that she turned his confession down. He argues back saying "Don't bullshit me. If that's true why did you give me such a nickname." He then yells at her saying she got what she deserved. This leaves Aki in despair and she replies that she thought Makabe would understand her. She leaves out crying.
In Chapter 39, after learning the truth from Yoshino, he quickly sprints to where Aki and Kanetsugu are. He finds them and confronts Kanetsugu and Aki. Finally, he tells Aki the truth about him being the Masamune she had befriended back then. After clearing the misunderstanding, and Kanetsugu running after being exposed, Aki tells him that she doesn't mind dating him which leaves him standing there, laughing to himself. They made up to each other afterwards and officially became a couple.
As a couple, the two are in a slightly awkward phase, with Aki becoming flustered when Masamune touched her and the two still calling each other as they have been before the identity revelation. Regardless, she is open to going on a date with Masamune on Christmas Eve, which is also her birthday, and behaves in direct contrast to their first date at the beginning of the series, such as wanting to sit next to Masamune at the movies. Masamune, who had doubts about his feelings towards Aki, begins to slowly acknowledge that they are indeed not false. However, he is bothered by Aki's interest in making him chubby like how he used to be, feeling uncertain if she is in love with the Masamune of the past as opposed to himself now.
He was a bit embarrassed when he found out that she transferred to his school only for him. He from then on for some chapters was flustered when he saw her, but soon was able to overcome it by giving more attention to Aki. When she invites him to her apartment, he tries to sneak in her room only to be later found out by Neko. She tells him she had indeed took his and Aki's childhood photo. When she said he was cute and didn't matter if he used to be fat he thought to himself that he might cry, which left him totally defenseless. She uses this chance to kiss him and seduce him on her bed. When he thought to himself that it didn't matter what ever happens, he suddenly remembers Aki's face and her saying that she can't come to like someone like him in his childhood which makes him stop Neko's any more advance on him. He tells her that he doesn't truly love her and doesn't want to be dishonest anymore.
She shows her true nature which is very kind nature by hiding the fact that she has a weak constitution. He understands this when she runs away from home after getting rejected by Masamune. It is also shown that she was his childhood friend because she had a photo taken with him and his family where she was fat. Even his family seems to remember her but Masamune is oblivious to all of this. She still seems to have not overcome his rejection, but tries to avoid any kindness Masamune directs towards her.
After Masamune and Aki begin dating, he feels doubts about truly having feelings for Aki, which Neko catches on despite his attempts to hide it. Neko says she will wait and see how things will unfold, implying that she believes that she might still have a chance to be with Masamune.
Love Rival Edit
Masamune doesn't know that Aki was fooled into becoming Gasou's fiancee or even about Kanetsugu being a female. Masamune sees her like a rival and challenges her for the place of Aki's dance partner. It is unknown on whether Masamune hates her or not although it is certain that he doesn't like her. He is frustrated by Aki's sudden attraction towards her and Aki choosing her. After Masamune and Aki become a couple, Masamune runs into Gasou while getting food for Aki. He learns about the circumstances of her previous actions and is happy to see that she is doing better off and is happier than before
They both are seen almost all the time together. He is Masamune's first friend. Shuri is very shy and always sticks to Masamune. As seen when Aki invites him to come with her to a private island. He panics in embarrassment because she is asking only him to come causing him to jump and hug Masamune while saying, "I won't go anywhere if Masamune is not coming.".
She is Aki's maid who is helping him succeed in his plan of humiliating Aki so she can reflect on her actions. She knows that he is the one from long time back who Aki nicknamed 'piggy'. He calls her master and she is seen helping him a lot but limiting herself trying not to overdo it. Even though in front it looks like she wants Masamune to succeed in his plan, it mostly looks like she wants them to become a real couple as only she knows that Aki used to love Masamune. The proof for this is that she avoided Masamune wavering his feelings towards Neko by telling him not to be taken away by tide.
She indirectly confesses to him in chapter 3 by asking him if he would like to hang out with her to movies and etc. to which he rejects. She cries and hopes they could be good friends from then on. Later, they seem to be on good terms.