
The original millennium earl disappeared and split into two children, Nea and Mana.
Mana slowly went insane and killed Nea because his mind kept telling him to kill him and become the one true Earl, he later went insane with grief and killed himself.
When a noah dies, they can revive later but their memories get damaged unless they find a host who can keep their memories safe until they revive in that host's body.
Nea knew Mana was gonna kill him so he found Allen who was a random soldier fighting in a war.
In exchange for being Nea's host, he gets to have a free wish.
The bookman clan is tasked with recording the history of the whole holy war and there can be only one bookman at a time.
Beta Lavi was supposed to inherit the bookman title but he got so fascinated by Nea, he abandoned his post and found Allen who was his host.
They traveled together for a while until Apocryphos (the guardian angel for innocence) attacked them.
He tried to make the helix of life consume Allen but Lavi jumped in to save him.
Allen was chosen by the innocence in this fight because it's drawn to people with tragic fates, he also slowly got consumed & reverted back to his childhood form
Lavi gets consumed by the helix and Allen is thrown out after 8 years of standstill.
Since there can be only one Lavi, once the beta one dies a new Lavi (our version) is born.
At this point, Mana gets revived but since he didn't have a host his memories got damaged & doesn't remember why he lost Nea (he doesn't remember killing Nea)
He joined the circus because he was hoping that Nea would come to see the show like everyone else does and reunites with Mana.
Apo erases all of freshly shrunken Allen's memories and sells him to a circus (not sure about this part but I think he was hoping that Allen & Mana would meet one day and Allen would kill him)
And exactly that happens, Apo manipulates a jealous performer in the circus to kill Mana's dog Allen (Mana probably remembered that name from his previous life but didn't realize it)
MC who's currently nameless, gets enraged and tries to attack the dog killer and unconsciously activates his innocence
Mana tries to stop him but Allen accidentally injures him which wakes up his inner Noah and becomes the Earl again.
After that, Mana becomes the Earl, kills everyone in the circus and completely goes insane after being calmed down by Cross.
He forgets everything and thinks MC is his dog Allen, MC doesn't correct him and they live together for a while until Mana dies in his sleep one day.
I'm not sure about the next part but Earl offers to bring Mana back and Allen accepts it, I'm kind of confused about this part because if Mana is the Earl then who are they reviving?
Whatever ''Mana'' curses MC and a little bit of his soul becomes Allen's cursed eye, he later kills Akuma Mana with his self activated innocence
Previous Lavi's soul finds Allen and becomes a part of him, turning Allen's hair white.
After that Cross finds him and makes him his student yada yada you know the rest.

Currently, Kanda & general Tiedoll are working together to see what happened to Mana's corpse (they found the coffin empty)
Allen & Johnny & Link are at the bookman mansion, trying to find out what happened in the past.
The short hair girl you see in the latest chapter gave Allen a poison that can show him his past before Apo remade him because they wanted to learn what happened to the old Lavi who abandoned his job for Allen.

Apocryphos didn't make the Helix of Life consume Allen.
Apocryphos tried to have Allen become the new host of the Heart/Vessel. And destroying Allen in the process.
The Helix of Life is something OG Lavi was studying. He used it to protect Allen from Apocryphos and the Heart.
OG Lavi merged with Allen in the process.
Mana did not Kill Nea because he went insane. The 14th (Nea) went Awol on the rest of the Noahs. He betrayed them for an unknown reason. The other Noahs believe he was trying to become the next Earl instead of Mana but Road knows something. She is the oldest Noah who was alive during the incident. In a flashback she is seen holding Mana away from Neah. Road and Neah were also lovers. The rest of the Noahs don't have all of their memories from when this incident happened. We have yet to really know why Nea did what he did (try to kill Mana etc).

Yeah after the recent chapters I realized I got some stuff wrong about Apo but I'm pretty sure Apo wasn't trying to make him into a vessel considering Allen was siding with Nea and he only got his innocence after he already dissolved into his childhood stage.
It makes no sense for him to try to turn a Noah sympathizer to the new vessel especially when he doesn't have an innocence and a clear hatred for Apo. If lavi didn't jump in, Allen would've died which Apo expressed anger towards.
If he wanted to make Allen into a new vessel why would he get angry when Lavi tried to save Allen from getting completely consumed?
I'm 100% sure he only decided to nurture Allen into becoming a vessel when he was out of the helix & got an innocence. He decided to wipe his memory and nurture him into becoming a good exorcist so he can hold the heart one day.
Also:
Didn't Nea kill every Noah except Road? that's why we saw them getting revived like we saw with Wisely? and that's why they called Nea a traitor and hated him? I doubt they would've hated him with this much passion if Nea just decided to fuck around.
Also I doubt Road and Nea had a thing going on considering Road is hostile towards Nea just like every other Noah and literally nobody knew about them dating (Desires was literally torturing Lavi to get that info out)
2 questions:
Aren't they all siblings / blood related?
Why would Road fall in love with Nea considering the situation they're in
I said Mana went insane and killed Nea because I'm pretty sure he wasn't 100% good in the head back then. There's absolutely no way Mana would kill Nea voluntarily. I was guessing that the Millenium side of him was trying to drive him insane so he could be controlled easier.
I've seen a lot of theories on Mana and Nea's rivalry and the most common one I see it that Nea was trying to protect Mana from becoming the Earl by killing him and becoming the Earl himself.

Yes! I went back to double check. So Apo tried to eliminate Allen because he was Nea's Host.
Lavi protected Allen and through that all three entities merged to create Allen's new body. Apo then did what he did.
It is true, Nea betrayed the Noah's. It's been a while so I can remember if they explicitly stated if he killed them and who he killed. You are probably correct. The Noah's believe that Nea did it to become the New Earl. But we have never really had confirmation about why Nea did what he did. In the latest chapters, OG Lavi stated that Nea was looking for the reason for his existence.
Road and Nea share a connection quite unlike he does with the other Noah's. I don't remember where I got the they were lovers from. It's like a 8+ years old memory now from way back when Allen first got captured by the Black Order. She is also the only survivor other than Mana of Nea's betrayal. Unsure if she survived by luck or because he let her go. All other Noah's are newer, younger incarnations. Their memories are imperfect. They don't actually remember all memories of all incarnation but their Noah memories do remember the hatred of innocence and the 14th's betrayal. One such example is Tyki Myk who has Nea's appearance but can't remember why.

Haha tbh the story is very long, confusing and hard to follow since chapters come out so late, nobody is 100% about anything yet.
One thing, I think Road and Nea's relationship is close to a forced alliance? I think they don't really like each other but they have to get along on some level because they both love and care for Mana.
Road said ''Nea fought for Mana'' so I'm guessing they tolerate each other's existence because of their position in the war.
If Nea is really strong enough to kill every Noah, there must be a reason why Road was left alone, maybe because she was the only person who cared about Mana rather than the Earl position, and he could trust her to look after Mana while he was fucking around.
She and Tykki seemed to be the only ones who actually showed sympathy towards Mana and his emotional nature rather than finding it weird like the other Noah.
Been reading this for so long I forgot the story and all confused. Someone please summarize it for me