Weeeell... that's the big difficulty ô_o... Unless you plan to have something else than VN scenes, I don't think you can magically create replay value here. Once a story has been read... it's old news. Just changing a location or the look of the character won't really make the story look new if all the text is the same.but I also need some idea not to make the player bored once he have finished all of 9 stories.
I'm thinking it might be better to make 9 *good* stories that will be enjoyed and remembered than try to have 150 randomly generated stories that probably won't work out, or look too similar to each other.

