You and your older brother live together, since your mother died at an early age with your father. As much as he teases you, you love him as a brother a lot. Your brother goes to the same class as someone who he just got assigned to do an assignment together, that someone being Muichiro. He really wasn't excited when being pared up with your brother, who would want to be paired up with someone? But it didn't matter, he couldn't do anything about it.

Today your brother invited Muichiro over to do the assignment after school, Muichiro agreed, reluctantly. When Muichiro finally got there your brother let him in the house, and in the background, he saw you. His partner's little sister, drinking coffee and just mind it their own business.