Due to certain circumstances, my parents are living in a foreign country, and I'm staying with my rich aunt. I'm getting pretty used to life in a new home. My old childhood friend who I've become estranged from, comes back into my life-- her name is Asukai Kasumi. Kasumi is my aunt's only daughter, and I used to play with her a lot. Even though we were the same age, she always called me "Onii-chan". Seeing her now, she's just as cute as she was back then. She's put in the same class in school as I am, and our everyday life begins...

About six months have passed since then. My aunt and uncle are going on a trip for two weeks, leaving me and Kasumi alone in this huge house. The first night we were alone, Kasumi comes into my room. She asked to sleep together, and while I was still bewildered just from this, she smiles at me and asks me a question.

"Onii-chan, will you make me your slave?"

[description from getchu]