Yuma, a high school girl who has just gotten her first boyfriend, is experiencing thrilling days. When she seeks dating advice from her childhood friend, the popular and beautiful girl Hotaru, she finds herself being teased for her lack of experience. To Yuma's surprise, Hotaru playfully initiates kisses and other intimate actions. Even during a double date with their boyfriends, Hotaru pushes the boundaries by touching Yuma and trying things that Yuma hasn't even done with her own boyfriend...?! As Yuma becomes increasingly aware of the various unspoken situations with Hotaru's boyfriend, she realizes that she is gradually getting drawn into a complicated relationship. This is the secret A to Z of the two high school girls after school. Will their relationship be discovered, or will they manage to keep it hidden...?