For years, ordinary high-schooler Kousaka Kyousuke has had an icy relationship with his younger sister Kirino, a star athlete who is also a star student.

While being grilled by Kirino over why he hasn't made any progress in the game she ordered him to complete, it occurs to Kyousuke that she needs some friends that she can talk to without concealing her otaku interests.

Kirino finds her first otaku friends at the IRL meet: "Kuroneko" and "Saori Bajeena." They spend their days deep in discussions over their otaku interests. Seeing Kirino this way puts Kyousuke's mind at ease.

One day, Kirino's non-otaku, "public" friends—Aragaki Ayase and Kurusu Nanako—come over to visit. Kyousuke is harshly told by Kirino to not let her friends see him.

On the way home from an enjoyable Summerket. They bump into Aragaki Ayase, Kirino's best friend.

Kyousuke is asked about his relationship with Manami by his friend, Akagi. Akagi is exasperated when Kyousuke answers that, although they don't have a romantic relationship, he doesn't want her to be taken by anyone else.

Kyousuke comes home one day and is startled to find Kuroneko loitering in the living room by herself.

Kirino has made her debut as an author. Reader response has been overwhelming, and her editor has even better news to report.

Kirino has been acting strangely antsy for the past few days. The reason is that the little sister game she ordered hasn't arrived yet.

One day, Ayase calls Kyousuke out of the blue and asks him to see her. She wants to get Kirino a present, and wants him to think of what she would be happiest to get.

Sent out to buy groceries by his mother, Kyousuke bumps into Manami at the supermarket. They get to talking, and they eventually arrange for Manami to come visit for the first time in ages.

Ever since the events of the previous episode, Kyousuke has been nervous about his improved relationship with his sister.

Kuroneko (real name: Ruri Gokou) enrolls in Kyousuke's school, and Saori feels downhearted that she hasn't heard from Kirino. Kyousuke notices that Ruri is having trouble making friends due to her personality, so he decides they should try a membership at their school's Games Research club where the boy meets two other persons he never expected to be there as well.

With Sena and Kuroneko constantly quarreling in the Games Development club, the club president decides they'll have to write a game together and submit it to an online contest. Both girls have different concepts about the game's theme, so they'll both present them to the club whose members will then decide by majority vote whose concept will have to be implemented. And Kyousuke, with no programming skills thus acting as supervisor for the team, suggests to write an eroge—in order to have less competition and a better chance to win the contest.

As Ruri and Sena's game is bashed on the Internet they decide to work harder towards making a better game. As Kyousuke prepares to go home he receives a text message from Kirino telling him to throw away her collection of eroge and anime goods! Kyousuke contacts Ayase who confirms Kirino hasn't been in contact with her since she left either. Kyousuke then meets up with Ruri who encourages him to fly to America to find the root of Kirino's problem—and before the boy leaves she puts a special jinx on him.