There's just too much vagueness in the game, and the only evidence that is certain is in that Japanese book they released recently, they said Nero was Vergil's child.
That's fine and all, but if they were intent on making Nero Vergil's son, why did they wait years later and then release this important information in a book that not many people outside Japan would be able to get their hands on, let alone read and understand it. Heck, even the Japanese book was vague. It just used the kanji 'ko' for child.
As for Nero and his name, they were going to call him Rodan according to one of the concept books. I don't know why they decided to change the name to Nero. Edit: Just looked it up, apparently Morihashi Bingo came up with Nero by accident, and it doesn't have anything to do with Nelo Angelo....weird. Talk about just throwing things together. There was me thinking there was some kind of planning and thought went into naming characters. Nope, it was an accident that Nero was called Nero. :facepalm:
That pretty much sums up this whole Vergil, is he, isn't he Nero's father. It's like Capcom just needed a convenient way to explain Nero and went with whatever they felt like for the sake of it. The best part is, we find out this information in a novel that isn't exactly cannon, and the concrete evidence in that concept book which pretty much spells it out. But in doing so, they disregard Vergil's personality and the timeline just to throw these ideas together.
I don't think it was an actual "accident" that his name became Nero since his name ties quite well in with the events of DMC4 and the historical tragedy of the destruction of Rome and the burning of Christians at the hand of Roman Emperor Nero.
It ties in so well due to that fact how the actual events are referenced or mentioned in the Bible in the book of Revelations and how the author for that book was Paul who lived during that event wrote the book as a hope that their savior would return and save them during such dark times. Not only that but when people refer to the Antichrist and the Mark of the Beast it all ties back to Emperor Nero since his full name (too long to remember and too lazy to look up) when translated through the Hebraic numeric system is equal to 666. So 666 mean Nero or his full name. So when the Bible refers to the Antichrists its referring to Emperor Nero.
In DMC4, there are tons of parallels to this. Fortuna City is basically a lot of like Rome in design and concept and what happened to Fortuna City it was wrecked by demons whereas Rome was destroyed by Emperor Nero's negligence or own fault which is funny due to the fact the reason why the demons were unleashed on Fortuna City was due to Nero's own irrationality and fault which led him to be captured and used to cause Fortuna's City to be destroyed. Both didn't purposely caused their own cities to be damaged but did. Not only that there is the burning of Christians or better yet the slaughtering of the towns people at the hands of the demons (that Nero in a way unleashed and also parallels to Emperor Nero causing said Christians to be executed) and the people or followers of the Order of the Sword are basically designed and styled after Christians especially the entire religion itself with Sparda being Jesus as their savior. Then there is the return of the "Savior". In the book it was mostly what Paul and many Christians at the time (and still today) wanted when in such dark and tribulatious times but it never came true and has yet came true same way how the Savior in DMC4 was merely false and a giant demon.
Also, more connections to the Book of Revelations are the various beasts and animals in it like the 3 demon bosses such as Berial, Dagon/Bael, and Echidna being designed after the beasts that appears in that book such as frogs being used to spread lies and deceit same way how Dagon/Bael used those fishing lores to deceive Nero and Dante and Berial and Echinda could be those gigantic beasts that fought along side Satan and the forces of evil.
There are other elements that ties into the Book of Revelations and various "End Times" theories.
The entire plot of DMC4 was basically the Order of the Sword creating the Book of Revelations in real life...well in the DMC world.
Its too much of a coincidence that Nero's name was just an "accident" unless it was and they basically decided to revolve the entire story around that "accident" or the story was already like that and they thought to rename him Nero since it seems more fitting.
Actually if they never named him Nero I never would've saw the parallels to the Burning of Rome, Execution of Christians, and Emperor Nero and the Book of Revelations.