Masaki's older sister, Miyuki, was involved in a traffic accident.
She hit her head hard and was unconscious for two days, but thanks to the Masaki's care, she was able to be released from the hospital just one week later.
The night he was released from the hospital, Miyuki suddenly tried to rape him.
Masaki was carried away and ended up having sex with her.
Thinking something was wrong, he talked to her, and found out that the aftereffects had left her with a split personality.
Which older sister will you choose: the same old ``big sister'' or the sexy ``big sister''?