Building Six: The Siblings' Multiplication.Haruki arrives home and Mutsuki offers to help him with his homework. He turns her down because she is bad at teaching (he doesn't tell her this). Helping Yayoi prepare for a math exam, he deduces that her problem is in her grasp of multiplication. When bedtime comes, she is still having trouble. The next day, when she returns from school, she refuses to show Haruki her test results. After a brief struggle, they fall and he lands on top of her, just as Mutsuki walks in, causing a misunderstanding.