Childhood friends Madoka and Tatsuya are dating in secret from their parents. They had hoped their relationship would last forever, but it falls apart when their parents remarry. Their relationship is torn apart by their status as siblings. Though they live under the same roof, they feel each other's presence is far away. Tatsuya's female classmate finds a way to get close to him. Jealous, Madoka pressures Tatsuya into a physical relationship again. The two secretly become lovers again. However, their happy time is short-lived, as their parents find out about their relationship and urge them to break up. Madoka runs out of the house, and Tatsuya chases after her. They end up on a beach where they swear eternal love to each other... The two childhood friends continue to have creampie sex without their parents knowing, living the daily life of a blue, twisted, forbidden love.