Currently there are no guides.
The last stage is 1-20, you should have seen a message at the end of story singaling that
All characters who have 2nd stages get them only during combat. They don't have a dedicated scene to it. Though Maria does grow during her Bond dialogue.
Narrator-chan is Patreon exclusive. You need to be of the Growth Connoisseur tier on my patreon then authenticate inside the game. She will appear as an item inside your inventory if you do that.