Try building up trust between Mariko and Shira, and then don't show her the book. :) Glad to hear you've enjoyed the game!
Thank you so much! That got me the silver clue but I'm still having trouble with the orange one if I could just get one more hint! :)
(EDIT: Nevermind, I was just getting the hint wrong, haha)
(EDIT2: ...and now I'm stuck on how to get anything but Shirr's Bad Endings A and B. The walkthrough cannot come fast enough)