I thought we were talking about stories that had ended already?

[He knows it's not quite the same. There's little that connects him anymore to any Keiichi one could find in those worlds. He only has connections with one and that one vanished a long time ago to become Primo. It's easier to consider it the end of a book and close it, even if the story continues through other volumes.]

Still, I suppose there are stories long enough to actually need several books. So when a part ends, and the book comes to be closed, there's yet another book opening in order to continue the story.