Summary
Yuuto and Erika start living independently after their father’s job transfer to Sapporo. Although they are siblings, they are not biologically related; Yuuto’s widowed father married Erika’s mother. As they navigate their new living situation, Yuuto and Erika develop a sexual relationship. However, Yuuto’s art teacher, Sayaka Ichinose, observes the shift in their behavior and becomes curious about what is happening.