If you associate with vermillion (red)

A story about an ordinary me and my younger sister who only imitates me. I, Hinata Aoi, have a younger sister named Kanae. Kanae has been imitating me ever since she was conscious of the world, but that hasn't changed even now that she's in high school. When I became a university student, I got a boyfriend named Kasugai Tomoki. When Kanae found out about this, she insisted on meeting him, so I decided to introduce them, but...