Haruka Takayama and Yuu Sonoda are two best friends who are just starting high school together. However, as the school year starts and the two starting making new friends, Haruka worries that her friendship with Yuu will stop being special. After Yuu suggests that the two of them do something that is unique to them, Haruka suggests they start kissing each other in secret as proof of their special friendship. Later, Haruka and Yuu get locked inside an empty classroom whilst they were kissing on the veranda, requiring them to cross a large gap between verandas to get to the neighbouring classroom.

The girls decide to sleep over at school in order to complete their preparations for the cultural festival. During the nighttime, Shizuku gets to spend some time with Kotone, whillst Haruka and Yuu also have some time together. On the day of the festival, after a successful performance, Haruka goes around the festival with Kaede and Yuzu, where Kaede explains why she chose to become the class representative. Haruka and Yuu then spend the rest of the festival together, kissing all the while.

Haruka invites Yuu to join her in attending a relative's wedding, which Yuu misinterprets as Haruka asking her to marry her. Although Yuu is disappointed that this is not the case, Haruka becomes touched by the thought of it. On Christmas Eve, Mitsuki joins Haruka and the others in visiting the Christmas lights, noticing that Haruka and Yuu seem to be shying away from each other. After Haruka and Yuu become separated from the others, Haruka reveals she had been shy to look Yuu in the face because of the strong feelings she's been having, with Yuu replying she had felt the same.

On a snowy day, Haruka and Shizuku go outside to have their lunch, though soon find it a bit too cold. As Shizuku dreads the day when she'll have to part ways with Kotone, Haruka brings Kotone over to cheer her up, encouraging everyone else to come out for a snowball fight. Meanwhile, Kaede mentions to Mitsuki how she believes Haruka and Yuu are dating. Later during gym, Haruka feels the need to compete against Kaede in jumprope, only for her group to end up coming last and having to clear up the equipment. As Haruka offers to do it alone and the others leave, the teacher assumes they were finished and ends up locking Haruka in the gym storage. Learning of Haruka's disappearance, the girls set up a ladder to the gym storage's window, where Yuu manages to get a kiss with Haruka, before they manage to get the door unlocked.

The graduation party for Mitsuki and Rina gets underway, with everyone giving them presents. During the party, as Yuu gets into an argument with Mitsuki over her kissing relationship with Haruka, Mitsuki, upon hearing that their kissing is part of a 'special friendship', confesses her love to Haruka. Following the graduation ceremony, Haruka is called about Mitsuki, who discovers Haruka knows nothing about love or dating and misinterpreted Mitsuki's confession. Haruka ends up rejecting Mitsuki, who leaves her with just a kiss on the forehead. Yuu, who had been watching them, bring Haruka to the old classroom, where they kiss whilst telling each other they love each other. With their feelings stronger than ever, Haruka and Yuu begin their second year of school.