Perhaps a little more clarification is in order, regarding that timeline.
The original Needless story was a 2000 page doujin written way back when Imai was still at school, and other than a few images on the artist's website, no one apart from his friends and family has ever seen it. It falls into two parts, with two different protagonists:
Needless 1: Adam Blade (male)
Needless 2: Adam Neuschwanstein (female)
(because it's a pain typing all that, we shortened it to ANn...)
The current Needless story is based on this doujin, but how closely (or not) is anyone's guess. According to the author, Cruz, Arca, Saten and Uten are all new characters, which I suspect has made quite a difference to the plot... BTW, the diagram posted by Adan was published about the same time as chapter 40, and the story is now (probably) approaching the end of part 1.
Later came another doujin called
BLACK SPOT which features characters called Cain and Abel. You can read the first 2 chapters on the website, and apparently the book is (or was) available to buy... but AFAICT it isn't canon as far as the current story is concerned.
The professional publication of Needless in Ultra Jump started with a number of one-shots which were later collected into a volume titled Needless Zero. Its contents are:
- Needless 1.5 - the prologue to Needless 2, introducing Cain and ANn.
- Sacred Sword of the Reaper ("Death god's holy sword" in the diagram above) - prologue to Needless 1, introducing Blade.
- Second Sight - none of the characters from this story have appeared in Needless 1. It remains to be seen whether any of them will turn up in part 2.
- Egoic Lotus - ditto.
After Needless proper began serialisation, several more side stories were published, and these were collected into
another Zero volume, Needless Zero II. (You can see how all these numbers might cause confusion...) Its contents:
- Genesis
- Burning Knuckle
- Killer Girls
- Horror House
- Goldilocks - not shown in the diagram, follows chapter 16
- Fire Diamond - precedes the main story
I think that covers everything. Hope it helps.
