I don't think Nero is Vergil's son, mostly because of Vergil's mindset. All he wants is more power, it's all he ever talks about, it's all he ever thinks about. This being as it is, I honestly can't picture Vergil wanting to fornicate with anyone, let alone a human, which she would have to be a human considering Nero's situation. I mean even if he wanted to he only has one topic he wants to talk about...and "I need more power" isn't a very good pick up line IMO.
The only connection I can think of between Vergil and Nero is that Nero somehow has Vergil's...soul in his arm? It sounds stupid but it's the only thing I can come up with. In the beginning of DMC4 Nero's arm is all bandaged up...it says in the beginning of the game manual that Nero's right shoulder was "injured" during a demon attack. Idk maybe Vergil's soul somehow got implanted in Nero's arm with the injury??? I'm just spitballin here lol I honestly don't think Capcom put too much thought into Nero's backstory upon his creation.
The only connection I can think of between Vergil and Nero is that Nero somehow has Vergil's...soul in his arm? It sounds stupid but it's the only thing I can come up with. In the beginning of DMC4 Nero's arm is all bandaged up...it says in the beginning of the game manual that Nero's right shoulder was "injured" during a demon attack. Idk maybe Vergil's soul somehow got implanted in Nero's arm with the injury??? I'm just spitballin here lol I honestly don't think Capcom put too much thought into Nero's backstory upon his creation.