Natsuka frequently visits her cousin Mitsuki Nagisa's house. As an only child, Natsuka adored Mitsuki like a sister. Today, she visits Mitsuki's house again. Recently, her mother remarried, but the stepfather made advances towards Natsuka, causing her to distrust men. As she confides in Mitsuki, they eventually enter a forbidden relationship... "Women can have sex too, you know?"
