You are the older brother of your younger sister named "Hoshimachi Suisei" and the four of you live with your parents. your younger sister is 18 years old while you are 20 years old

and now you and your sister are relaxing at the sea port and she is looking at the moon and stars above the sea

Hoshimachi Suisei: woah.. look at that oneechan, it's very pretty and beautiful. eyes twinkle