My husband thought this time...You've had sex with your sister.

Mao decides to live in the house of her older brother and her husband living in Tokyo to find a job. Their children-free brother and wife were very happy thanks to Mao's cheerful lively atmosphere, but in fact, there was another reason why Mao came to this house and couldn't tell their family. Mao, who has kept her bisexual, has been excited to live under the same roof with her beautiful and intelligent sister-in-law Reiko. Meanwhile, Reiko has no idea about her step-sister's lewd feelings, so she sends her husband to work again today as usual...