● Most of the first chaptes are Kanda and Johnny looking for Allen.
● When he is found, Tiky and Wisely attack them and Nea finally takes control of Allen.
● Still, Nea can't keep it for much, and Allen manages to be back to himself. That's where some chapters later, the Earl shows up.
● When they start to fight, the Earl seems to be out of his senses and keeps calling Allen "Nea" while they fight.
● On the middle of all of it, Allen and the Earl start to have flashbacks/lose their senses together, becoming "Nea" and "Mana" (the brothers) at the end of it.
● Nea (Allen) and Mana ("Earl") hug each other and start to talk, but Mana doesn't understand why he misses and cries so much for Nea, if he doesn't even remember him.
● Nea (Allen) starts then to explain to him that they were twin brothers once in the past , but as the flashbacks start to open more and more, it's revealed that both Nea and Mana were originally one being, called the Millenium Earl, and this being divided in two parts becoming the twin brothers. The difference was, that Nea was the only Noah able to remember, Mana then knew of this too, but after killing Nea to become the Millenium Earl himself, he was in so much despair and regret that his own brain started to seal up the bad memories, giving brith to the Mana that Allen knew.
The new Mana then somehow had a soul, and when this new Mana died, the soul separated, the body noafied and again, it gave birth to the Millenium Earl that we know, who had forgotten that he was Mana.
Basically: the Millenuim Earl we know (the main antagonist) is Mana without memories, who is Nea's other half and later Allen's adoptive father at the circus. But he forgot all of this by killing his other half/Nea.
So in summary:
1. Mana + Nea= Millenium Earl
2. Millenium Earl divides itself = two beings named Mana and Nea.
3. Mana kills Nea.
4. Mana becomes crazy from this and loses his memories.
5. Mana meets a child at the circus and he names him Allen and becomes his adoptive son.
6. One more time, Mana loses his senses and becomes the antagonist we as the reader know, that's it, the chubby smiling demon named the Earl.
6. It's revelaed at some time that Allen=Nea.
7. The conclusion is: if Mana (the Earl)=Nea (Allen), that means that the Earl (our main antagonist)=Allen (our main character).
● After aaaaall of this, Mana becomes mad/out of his senses again, refusing to believe him and attacks Nea (Allen) but Link rescues him.
● This is the part of the arc where while Nea is going around in his body, Allen is trapped/walking in Nea's mental inner world.
● Marian Cross's image shows up and explains to Allen that he will disappear soon, that the identity known as Allen Walker will disappear from this world in little time and only Nea will remain. Allen then remembers Lenalee (my ship *fangirl scream*) and refuses that to happen.
● Tikky and the rest go to get Nea , but when he's about to leave with them, Allen takes control of his own body again.
● When they are supposedily safe from danger, Allen still wants to escape fearing that he's dangerous to everyone. In the middle of this, Kanda reveals to him that Timcanpy died/was destroyed in the middle of a fight they had before (

).
● When Allen opens a gate to escape (yes... again) Kanda rushes and his taken with him as well.
● Both of them end up in the location next to the grave of the dog that belonged to Mana, whose name was Allen (that's literally why our MC is called like that lol), and after arguing and fightnig all over again, Allen begins to tell his story to Kanda, about his childhood in the circus and how he met the Mana that worked as a clown and became his father figure.
● On everything that the flashbacks has been going to far, Allen was a child abandoned by his parents because of his deformed arm. Allen, without
a name at that time and only called "Red", worked for a circus where he suffered abuse and hunger until he started to talk to Mana, the clown that only had a dog named "Allen" as a friend. Allen (our MC) became more and more friends with Mana, and when the dog is killed by some bitch, they decide to leave the circus together and work as wandering clowns.
Conclusion: I think that, based that we got two big important flashbacks showed (Nea/Mana's
and Allen's current one about his childhood), Hoshino's goal is to explain the gap between them at the end of the arc: how the phase between Nea and Allen was.