Familiarity. That's what it was. Vanitas and Roxas both saw somebody else in each other's faces. Their thoughts ran in tandem. If not him, then who? They're identical, so how?
Xion, ironically the only one not mistaken for another, broke the mutual silence. "Riku talked about you."
Vanitas crossed his arms and frowned. "Did he now. How nice of him to ruin an innocent outing."
"Innocent?! You trashed the place!" A simple sweep of the arm perfectly illustrated Roxas' point. The mansion's front garden was well and truly ruined.
"And I got rid of the Heartless! I made your lives easier, so what's the problem?!"
"The problem is you ruining Sora's name!" Roxas yelled, now. Defensive, weren't we?
"And what do you care about Sora's name? Shouldn't you be glad he's gone?"
Within the second, Roxas drew his twin blades. "That's it! How dare you? How dare you show yourself like it's nothing? How dare you parade around without a care in the world?!"
The by now trusty Ultima flashed in Vanitas' grip. "Is that's how it's gonna be? You'll attack me just for looking like somebody else?" A low blow, he knew, but those were his favourite. "Hypocritical, isn't it?"
Wrong thing to say, just as Vanitas expected. However, provoking his opponent was just what he wanted. He craved a real fight to test his new skills. Those Heartless weren't enough