Spoiler warning
1) There are four Death Notes that enter the human realm in the main series, and one in the one-shot chapter.
a) Sidoh's (the one Ryuk found in the Shinigami realm and gave to Light, with "Death Note" written on the cover)
b) Jealous's (the Shinigami who sacrificed his life to save Misa. Rem gives this one to Misa, and Misa later sends it to Mikami)
c) Rem's (Light takes it from her remains)
d) Ryuk's, which he doesn't use until the end of the series when he kills Light.
e) Meadra's, which she gives to the unnamed Death Note user in the one-shot chapter, set three years after Light's death. It appears to have a simple black cover, like Rem's.
2) What happened to each Death Note?
a) Sidoh's was given back to Sidoh after Light's dad dies.
b) Jealous's was burned up by Near, who stole it from Mikami.
"And the notebook that Aizawa brought here from the NPA headquarters... [Is it] real?"
c) Rem's is a mystery. Light and co. had been keeping it in a safe, and they supposedly brought it to the warehouse during the confrontation with Near, but Light implies that he replaced that notebook with a fake, and hid the real notebook, before they came to the warehouse. It could have been a bluff, but doesn't it make sense that he would want to hide his last remaining Death Note instead of leaving the chance that Near could take it?
Tsugumi Ohba addresses this topic in the How to Read 13 guide book, but gives no definite answer. Ohba's exact words are, "My theory is that Light secretly replaced [the notebook] with a fake and was hiding it." Kind of a cop-out with the "my theory" part, but if Ohba feels that way, I think it's safe to say that's what happened.
Anyway, if they indeed did bring the genuine notebook to the warehouse, Near burned that one as well. Otherwise, it's probably buried in the woods.
d) Ryuk's obviously stays with Ryuk when he goes back to the Shinigami realm.
e) Meadra takes her Death Note back to the Shinigami realm after the owner inexplicably writes his own name into the Death Note. She tosses the notebook to Ryuk because she didn't need it anymore.
3) The fake rules were written in Sidoh's Death Note, which also had all of the original rules Ryuk wrote (again, this is the notebook Ryuk dropped and Light picked up).
Yeah, I tend to go all out with my answers. But I'm a Death Note fanatic.
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