Non-boss as in the characters that are available at the start and boss characters are characters like Iku and Tenshi in swr.
And if I remember right you couldn't play as Iku and Tenshi until you beat story mode in swr so they don't want spoil characters so you can be surprised when you reach them in story mode.
And if I remember right you couldn't play as Iku and Tenshi until you beat story mode in swr so they don't want spoil characters so you can be surprised when you reach them in story mode.