We actually see the difference with Vergil wanting more power, with Nero turning it down at the end when he tries to give Dante back the Yamato. Nero has protected Kyrie and he no longer feels that he needs more power.

Their motivation to have power is actually kind of same. Vergil wants it so he can protect what he wants to protect(unlike when he was a kid and his mother died without him able to fight back at all) and Nero wants power to protect Kyrie.

The difference between them is that Vergil was twisted because of his failure to save Eva. Nero on the other hand, didn't fail to save Kyrie which makes him realize that power isn't everything.

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