@Dante Redgrave
Last time I checked...Nero can't go a full body DT (or transform into a demon) like Dante or Vergil, who are half demons. I mean when he gets Yamato, a Devil Arm, instead the soul of the sword comes out instead. (Some can say that ITS Vergil's soul or the soul of Yamato considering that Devil Arms are really the souls of powerful demons manifested in a physical weapon form. Then does Rebellion and Yamato have a soul to them and so were Dante's and Vergil's respective weapons demons at one point or specially made for them?).
Anyway, I see Nero's demon arm as a result as a failed Devil Trigger for if he was more demon than Dante and Vergil he could go into a full DT state like Lucia (who is a full demon) can easily do without Devil Arms (unless those blades are Devil Arms but I doubt it)...because as hinted in gameplay mechanics...the more demon you are (or the more demonic you become) the easier it is to go Devil Trigger without a Devil Arm.
Plus look at Lucia and Trish, both are full demons and aren't spouting demon growth defects. Plus Nero's arm started changing after he received an injury from a demon attack or a demon related incident so its not like his arm became that funky out of the blue. Its unknown why he has that arm and mixed with all the unclear and implied factors of DMC4's story...anything is possible.
Plus when was it said that Nero was turning into a demon....Nero who doesn't know what is going on just says "Yup I have a demonic arm.....I must be turning into a demon....I don't know why but I'm probably turning into a demon...no clarification just assumption" or was it Agnus who is just as confused as we are who assumes Nero is a demon and not only that said he was a demon to make Kyrie scared of him. Plus I mean Lady in DMC3 constantly refers to Dante as a "demon" because he took multiple bullets to the head and never refer to him as a "half-demon". Its like calling someone who is half black...black...he is not black...he is half it. But that is not that just it, Berial who is a demon refers to Nero as a human and even after seeing Nero's demonic arm and getting his ass kicked by it didn't even reconsider that "Oh this kid is a demon." If anything he refers to him as an unique human.
I have more to say but wanna see yours and others reaction.