I just thought I'd post this again, because most people don't read old pages. My apologies if this isn't allowed.
This is what I know about Nero:
1. He is meant to resemble Sparda. Sparda wore purple, Nero wears blue and red, which make purple. He loves a priestess just like Sparda did... it's basically the same story as that of Sparda.
Nero has the Devil Bringer arm, which is also red and blue. This leads me to believe the arm is Nero's own arm, NOT Vergil's, since Vergil's arm would only be blue, not red AND blue.
I don't think Vergil is 'inside Nero's arm', because how can a spirit be housed inside someone's arm?
Also, note that the spirit floating behind Nero seems to be Vergil, but isn't. If you look at Nero's full DT (my avatar), you'll notice that it looks exactly like the apparition (except for the blue color). It's actually quite likely Nero's DT is a fusion of Vergil's DT and his own.
2. He can't be Vergil's or Dante's son, since Dante is 29 in DMC4. This means Vergil would be 29 too. Since Nero is about 17 in DMC4, that would mean Vergil had sex with a human (which is doubtful) at the age of twelve (which is even less probable).
Another possibility is that Dante and Vergil are much older than 29; they are part demon after all. But I don't think this is the case, since Sparda remained in the human realm and fathered Dante and Vergil (in say 1975), and as far as I know, it's somewhere in the 2000s when Dante meets Nero.
3. He's had the blood of Sparda since birth. He's always had the white hair that the Sparda bloodline is renowned for. According to something I read, Nero's adoptive parents chose him because of his white hair, since it reminded them of their god, Sparda (the DMC novel is supposed to state this).
4. He may have been intended to be a half-demon like Dante and Vergil, since his concept art shows him sporting a full-body Devil Trigger (see my avatar, that's it). I read that only full demons and half-demons can have their own full Devil Trigger, so, since Capcom created full-body DT for Nero, that might mean that he's a half-demon, not a quarter demon like he should be if he's Vergil's son.
So the possibilities that we're left with are:
- Nero is the son of a relative of Sparda's and a human. This would make him a half-demon like Dante, though possibly less powerful.
- Sparda had a child with someone other than Eva. Probably not possible, since he died before Dante and Vergil were born, meaning Nero would have to be older than D&V. Besides, Sparda's a 'one girl' type of guy.
- Maybe he wasn't ''left on the steps of the orphanage'', (sounds suspicious) but he was created by somebody, perhaps by an unknown scientist. It can't be Agnus, since he knew nothing about Nero's powers.
- He could be the reincarnation of Sparda, but with Sanctus blurting out that Nero ''carries the blood of Sparda'' and that he's a ''descendant of Sparda's blood'', this theory seems impossible, as reincarnations don't have the same blood.
- He could be the descendant of Sparda and his previous wife (if he had one). That means he could be a half-demon like D&V. Not likely, as Sparda and Eva's relationship was legendary, but that one must not have been.
It's told that Sparda was the feudal lord of Fortuna, so yeah, a lot of Sparda stuff going on.
Feel free to comment/point out flaws. Thanks!