A group of four who were always together, but there's no longer a place for me there.
you, Homura, Nagisa, and Shion had been together since childhood.
But after entering high school, the distance between you and the other three gradually widened, and by the time they were sophomores, you's place had completely disappeared.
When planning things, the conversation progresses and decisions are made without you. No one even notices if you isn't there.
Nobody dislikes you, and they'll respond normally if spoken to, but even when the four are together, you can't break into the atmosphere of the other three, unconsciously feeling a sense of alienation.