Yuzu and her friends met and discuss relationships, which Yuzu intends to have one when she gets transferred to the new school. The next day, she preps her up for her first day of school. Unknowingly, she is attending an all-girls school with a strict dress code. The student council spotted Yuzu and bickered with other council members until their President, Mei, confronts and gropes her to confiscate her smartphone. Yuzu tries to get along with her classmates but to no avail, until Harumi helps her and tells about the rules of the school. As she explores the campus ...

As Yuzu remains bewildered by Mei's actions towards her, she gets on bad terms with the school's chairman, Mei's grandfather. She and Harumi then overhear Amamiya, Mei's alleged fiancée, speaking with his own lover and is just marrying Mei for her money and status. Despite Mei stating that she already knows and doesn't care, Yuzu notices her crying in her sleep over her father. The next day, Yuzu takes the stage to publicly announce Amamiya's affair in front of the whole school, using her status as the chairman's granddaughter to support her claims. That night, ...

Encouraged by Harumi, Yuzu decides to confront the chairman but finds him collapsed on the floor, deciding to take him to hospital. Thankful for Yuzu's help, the chairman decides to revoke her expulsion and allows Mei to live how she chooses to, leading her to return back to Yuzu's home. Later, as Yuzu becomes conflicted between her feelings for Mei and her role as a sister, she becomes upset when Mei states that the kiss between them was just a means of shutting her up. The next day, as Mei confronts Yuzu about a yuri incest manga amongst her belongings, Yuzu kisses ...

As Yuzu avoids coming home out of fear of having to face Mei, she is approached by Himeko, who is Mei's childhood friend, about what their relationship is. After telling Yuzu about how Mei's father left her, Himeko lies about Mei being hurt by Yuzu's actions, leading her to feel guilty until she runs into Mei, who calls her by her first name and tells Himeko that they are now sisters. Later that night, Mei apologizes to Yuzu and gives her first mutual kiss. The next day, Himeko, jealous of how close Yuzu is to Mei, forces herself upon Mei and later brags about "...

After receiving some amusement park tickets from Harumi, Yuzu asks Mei to accompany her as she goes to meet her father. Along the way, Mei tells Yuzu that nothing happened between her and Himeko, who gets told off by her when she tries to interrupt their date. Yuzu eventually arrives at her father's grave, where Yuzu, noticing Mei's feelings about her own father, feels she should give up on her love and try to become an ideal sister instead. The next day, Mei collapses with a fever just before a student council meeting, so Yuzu urges Himeko to attend the meetings in ...

Mei seems to be at odds with Shou, who would rather travel the world than inherit the school like Mei had hoped. Having been raised by her father with that in mind, Mei, feeling she has no-one else to rely on, attempts to comfort herself physically with Yuzu, but Yuzu slaps her before things can go any further. The next day, after learning that Shou is setting off abroad yet again, Yuzu urges Mei to work hard for her own sake, encouraging her to see her father off. Later, as Yuzu and Mei's relationship starts to deepen, Yuzu's childhood friend, Matsuri Mizusawa, ...

Feeling downhearted after Mei tells her to end their kissing habits, Yuzu comes across her childhood friend, Matsuri Mizusawa, becoming perturbed when she hears about her dubious methods of earning money. After glancing through Yuzu's phone, Matsuri catches onto her crush on Mei and almost forces herself onto her until Yuzu receives a call from Mei. Noticing Mei across the street, Matsuri forces a kiss upon Yuzu in front of her. The next day, Matsuri shows up at Yuzu's school to invite Yuzu on a date, effectively declaring war against Mei.

After accepting Matsuri's forceful invitation to hang out after school, Yuzu takes Mei with her to meet Matsuri. Matsuri greets Mei with a cold stare, having believed she'd meet Yuzu alone, and then proceeds to drag Yozu around the shopping mall.

With her dislike of Yuzu and Mei's relationship, Matsuri uses the secret photo she took at the shopping mall to blackmail Mei. Meanwhile, Yuzu struggles to bake a cake for her first Christmas together with Mei.

While Mei was able to express her feelings on Christmas, Yuzu couldn't respond sincerely and their relationship grows more awkward. Later, Yuzu oversleeps and misses the train for the school trip, but runs into a pretty girl who also missed her train.

After Yuzu reunites with her class, she tries to talk to Mei about what happened on Christmas. However Mei tells her to forget about that night. Tachibana Nina witnesses their exchange, and resolves to help fulfill her sister's destiny.

Yuzu promises Nina that she'll support Sara, but she can't help but feel shaken after learning that the girl of Sara's dreams is Mei. Nina ignores all the attention she's drawing, desperately holding Yuzu back to keep her from going to Mei.