I think it's an important clue about Nero's origins

[UchihaClanLeader]

Remember mission 11? When the Savior catches Nero with his arm, comes Credo. Sanctus stabs him with Yamato, and Credo falls down, but Dante catches him. Dante says: I don't know. I bet this kid (Nero) still got some life in him.
Nero takes Sanctus with his DB, but he didn't manage to catch him, and Sanctus appears next to Nero and impales Yamato into the DB. And the DB deactivates.
Only Yamato can do that to the DB, remember in mission 1, in the fight between Nero and Dante, when Nero is forced to reveal his DB to block Dante's Stinger, and Rebellion didn't manage to stab the DB, but Yamato did manage.

 

[Crimson Devil]

That's why I still believe that Nero is Vergil, or something like that...
If he was Sparda himself he would have a bigger connection with Rebellion and Sparda (he used it in the end like if it was a normal sword)
If you pay attention on Nero's DT, you can see that like Vergil, his left arm has a sheath made for Yamato.

 

[UchihaClanLeader]

^ Yeah but it was an artwork with Nero's fledged demon and he's red and blue.

 

[Sparda™]

Simple.

The Devil Bringer has connections to the Yamato. We can't say a thing how or why - Capcom's fault - so let's wait for some more info in the future.