Ai Sayama, an exclusive actress for Tameike Goro, appears in this one-off film, a live-action adaptation of the original work by Torotoro Melto! Junpei shares a room with his older sister, a university student. Every night, his sister enjoys cosplay. One day, during a cosplay shoot, things escalate and she starts taking off her costume. Normally, he just gets annoyed, but he finally can't stand it any longer and secretly masturbates to a picture of his sister. Just before he cums, he thinks his sister will see him and get angry, but instead, he has sex with her for the first time in her special costume. And then, every day, she starts cosplaying for him.