Devil Arms can be... possessive, especially those handed down by blood. Yamato especially so given her abilities. It takes a special way of thinking to utilize her powers to the fullest.

[ Nero was a lot cruder and more open than Vergil. He took a bit after his uncle than his father, but, at his core, he still was closer to Vergil than he thought and the sword knew it. ]

That she accepted enough of you to become a part of you meant that you shared the same blood as her last wielder.