The diminutive Sota Tachibana goes with his stepsister Kaoru to her volleyball team made of abnormally tall girls. He is introduced to team members Julia McKenzie, Sakura Asakura, Kyouka Teshigawara, and his crush, Ayano Hasegawa. Kaoru tells Sota he will live in their dorm as their caretaker and coach.
Ayano turns Sota down, devastating him. When he tells Kaoru what happened, she confronts Ayano, who says she is only interested in sex. Sakura eavesdrops and then tells Julia and Kyouka that Sota is available. The three try to seduce him, but he ignores them. The three try to sneak into his room at night, but decide to compete to see who is allowed in. Ayano sneaks into his room and mocks him for being short, angering him into having rough sex with her, which was what she was aiming for. When they finish, he again tries to confess his feelings, but she leaves the room mid-sentence. Meanwhile, Sakura and Kyouko are still competing by playing cards while Julia has fallen asleep.
Sota notices they are one player short for a proper volleyball team, then the captain, Sanae Yamada, returns from dealing with family issues. Sota is surprised to find she is even shorter than him. The team goes shopping for groceries, then has a party in Sota’s room to celebrate Sanae’s return. Ayano embarrasses Sota by graphically describing the sex they had. When everyone falls asleep, Sota leaves the room to get some air, but Sanae follows and seduces him, saying she does not mind that he is sleeping with Ayano. After they have sex, she says she is willing to wait until he falls for her.
Sakura loses her glasses, and Sota returns them. She remembers doing bizarre comedy routines to ease her loneliness and how her short childhood friend, Takeshi, tried to join the volleyball team, only to quit and leave her for another girl. During a game, she is hit in the face by a volleyball and breaks her glasses, injuring her left eye. Sota takes her to the infirmary and treats her injury. She seduces him. Afterwards, she blackmails him by threatening to tell the others they had sex into doing a bizarre comedy routine in front of Sanae and Kaoru, humiliating him.
The girls play strip Mahjong (whoever gets the lowest score each round must remove an article of clothing) in the middle of the night except for Kyouka who refuses to play. Kaoru, who is quickly stripped to just her panties, wakes Sota up so he can play. They wager that whichever girl wins can do whatever they want with Sota that night, while if Sota wins, they must do his chores for a month. Ayano eventually gets bored and leaves the game. Kaoru wins in the end. She asks to share his bed. He tries to sleep, but she kisses him on the lips and dry humps him. She abruptly stops and leaves the room, leaving him shocked.
Kaoru just wants to forget about trying to seduce Sota, but when the others tease her, she angrily hurls a volleyball that strikes Kyouka. This exposes that Kyouka is wearing padding over her flat chest, making her run away in shame. Sota pursues her to a hotel where he assures that she is beautiful. She strips and orders him to massage her breasts, which escalates into them having sex. The next day, Kyouka embraces her masculine figure by no longer wearing padding and getting a boyish haircut, which makes Ayano hit on her.
The volleyball and basketball teams have booked the gym at the same time and refuse to share. Julia proposes they settle it with a basketball game, and if their team wins, she gets to spend the rest of the day with Sota. The volleyball team wins when Julia reveals she used to play basketball. Julia and Sota return to the dorm and have sex in the shower. The basketball captain asks Kaoru for permission to borrow Julia for an upcoming game. Sota contemplates that he has had sex with every member of the volleyball team except for Kaoru, then freaks out for even thinking sexual thoughts about his sister.