So the last three books 10-12 are almost impossible to get your hands on. Amazon will price any of the manga between $60 and $950. It has been finished but the last three books were just poorly circulated. Books-a-Million have the first 9 books available for around $20 for every three (they are in omnibuses which are three books in one) and the 10th stand alone. If you want the last two, you have to really dig for them. The original book series sells all 12 for around $40 used if you want to read them the old fashioned way (which I would recommend.)
Minor spoilers ahead but nothing that ruins the story
The author was originally planning on around 24-28 books, rather than 12 however he had trouble since it was marketed as a young adult series and the story was only going to get darker and Darren couldn't stay a kid forever. So he reworked book 11 to wrap things up in book 12 more neatly (book 11 was originally going to be called the cannibal king). He wanted to spend more time focusing on the distorted future world. He has said there is a slim chance he may continue the series in the future, which is why he wont give us any details on the original plan for the 11th book. It is very unlikely that he will come back to the series however since he is beginning to move away from young adult and fantasy-esque stories to begin with.
I kind of really don't like how everyone is like “aw what a sweet well behaved child!” All the time. Like she isn’t sweet and well behaved. She was abused. like all the positive traits she is getting praised for are the results of her abuse and it comes off as a little weird e.e
Honestly, that has been bothering for a while now...