I reckon it's just some special book or valuable trinket, but...
If I'm wrong and it's actually hidin' Kosuzu-dono's secret treasure... now, that'd be interestin'.
What if it's secret photos of her crush, or letters she couldn't send...?
*TEMPTED*
*TEMPTED*
Like a short story written by an eccentric who doesn't leave her shop much, or a first-person novel...
......
I might look if I was alone, though...
Poke around in other people's things, and ye'll get what ye deserve!