Allen's Cursed Eye evolves like an Akuma.
His cursed eye has been juxtaposed with the eye of a level 3 Akuma Eshi.
And Allen was compared to a soul of an Akuma by Cross Marian. And Mana's curse takes the form of a skull that resides in his head similar to an Akuma.
I think his eye will eventually become a level 4.
I think he will gain extra pupils similar to Yanda when using Mugen. I think it will allow Allen to see the Noah Memory.
Like how Kanda combines his healing power with Mugen I think Allen will combine his curse power with Crown Clown. I think he will create a weapon that can destroy all Akuma which will be a call back to his interaction with Jan.
With the reveal of Mana being the Earl it brings into question whose soul he summoned in the Akuma. I have a theory that it was the soul of the previous owner of Crown Clown.
During's Allen first mission it was revealed that Innocence can cause ghosts to manifest.
Although the Ghost of Mater turned out not to be a ghost a real ghost did appear from the victims of the Black Order's Innocence experiments to create more Exorcists.
Later on we see another example of a ring made out of Innocence turning a person into ghost, Mister Martin.
The ghost of the European Branch was able to possess people so I think the ghost of Crown Clown's previous owner possessed the Akuma.
Allen's eye activated when he destroyed "Mana" so he should have seen the the soul of the Akuma.
He saw the soul of Alma Kalma who had just become an Akuma.
She appeared whole so Mana's soul should have been whole as well.
Even if the soul had deteriorate Allen would see it's original form after destroying the Akuma. If Allen did indeed see Mana then it seems like a ghost is impersonating him which I think there is evidence of.
Whenever Allen is in danger and knocked unconscious his left eye wakes him up and Allen sees an apparition of Mana. This seems just like hallucination but I think it is the ghost.
We see it again when Nea starts to awaken his left eye stops the transformation.
Again we see a hallucination of Mana but I think it was the ghost again.
Tykki was revealed to have heard the name Mana before.
We found out Tykki heard Allen mention Mana when they fought at the Ark.
I'm guessing it was this scene since Allen's eye was activated. I think Allen saw the Mana apparition again but Hoshino omitted it because it will show that the Mana hallucination is not one at all and is not Mana.
I feel like examining Mana's curse could gives a few hints who the previous owner was. A spiral and the letter D appears in the pentagram. The D is in the same font in the manga title which seems significant.
It appears on the skull manifestation of the cursed eye. The D appears in the same spot where Allen's pentagram is above the eye. The spiral takes the form of a monocle which I think represents "The World of Black and White." Also the skull looks like an Akuma with notable differences It has an eye, an initial instead of a full name and a larger pentagram at the top of the skull instead of a small one in the middle.
Mana and Nea both have the inital D in their names which I think connects to the D intial in Allen's curse eye. I think it stands for Domini or Dominus from Anno Domini which goes along with the religious theme of the story. Domini means "Our Lord" and I think Caterina gave them that name in honor of the Earl since his other title is Lord Millennium. I think another meaning for D.Gray-man could be Lord Gray-man or Lord of the Gray-man. Maybe the ghost was a nobleman.
Although Allen's eye evolves like an Akuma it seems like it's the opposite. When Allen's eye evolved it drove him to kill Akuma.
Juxtaposing Akuma's need to kill humans.
One interesting thing to note is that Mana names appears in lower case in cursive while Claire appears in print in capital letters.
We see it's the same in a later chapter which I think is another hint Allen did not summon the real Mana. But we only ever seen two Akuma rituals of Mana and Claire. We know Claire's was legit while Mana's is in question.
