i had a question. in the guide it mentioned "have your own sketchbook". I've found cassandra's sketchbook but it doesn't seem to allow me to meet the requirements for the corresponding ending (ending #17). I assume cassandra's sketchbook, however, is still somehow tied to getting "your own sketchbook". what am i missing? what extra requirement is there for that? I assume i somehow get another sketchbook from the store but can't figure out how to get it to show up.