Well, it's hard to say for sure. It could be a rival manga enthusiast who wanted to have it for themselves or a thief looking to make a profit by selling it on the black market. There are so many possibilities!
Well, it could be a rival seeking power or someone with a personal vendetta against the empress. There are several possible suspects, and the author might keep us guessing until the end.
Well, it could be one of the rivals of the empress or someone with a hidden agenda. Maybe it's related to power struggles or personal vendettas. But it really depends on the specific plot and characters of the manga.