No.9327979 ViewReplyOriginalReport
so light buries what is originally misa's book, and gives his book to rem to give to yotsuba, as well as writing the fake rules.

After rem dies, light takes rem's book, and the police lock up the book with fake rules.

Misa then digs up what was originally light's book.

as Kira, light gives his notebook (rems book?) to his father to kill mello, and later reacquires it. Before this, he also borrows misa's book so he won't lose his memory.
Afterwards, the death god sidoh takes an unknown one of the books and flies off, so now there are only 2 again.

One of the remaining books goes under lockup, and misa has the other, which she later gives to X-kira.