Imôto no oppai: Pururi momi makuri(2007)

Etsuko, a university student, lives with her older brother, Kentaro. Kentaro works at a factory, earning money for their living expenses while saving for his sister's wedding. It was Etsuko's birthday that day. When Kentaro came home late, Etsuko was awake and waiting for him. After a drunk Etsuko fell asleep, Kentaro began to feel strange. Trying to suppress his excitement, he lay beside her. The next day, Kentaro couldn't stop thinking about Etsuko...