Multiple protagonists in a youth also play supporting roles in other people's stories. You can see all the beginnings and endings of their youth. A protagonist may have multiple stories, and may also act as the protagonist in multiple stories. The main plot of each person is the branch plot of the whole book. The main protagonist is Lin Xichen, who is also the youth of each of us.
Concept: We never own time, but only exist deeply as a part of time.