Natsuo has a crush on his high school teacher, Hina and to get past his feelings he goes on a group date and meets Rui, who he sleeps with, but things become more complicated when he finds that they will both become step-sisters.

Rui has transferred to Natsuo's school and they opt to act like strangers, but at lunch Natsuo stages an argument, which helps Rui make friends because their classmates get to see her personality.

Natsuo learned the truth about Hina's mysterious relationship. Following an intense encounter with her, Natsuo leaves home to cool off and establishes a connection with Rui.

Determined to end Hina’s affair, Natsuo and Rui take matters into their own hands. But things don’t go according to plan...

Rui makes a new friend with a notorious reputation — and an uncomfortable attraction to Natsuo.

Crime doesn’t pay and the punishment doesn’t always fit the crime — a lesson Natsuo experiences firsthand after ‘borrowing’ a book from the library.