"No. I never have." He replies, stroking her hair. "I never dared. But I've hidden long enough. Fear has made it a necessity for both of us to hide our faces and cloak our actions. But what sort of way is that to live?" Nunally can't see, but he's looking directly at Shiki, and his tone almost challenging. "If I don't stop running, I'll never stop. I'll spend my entire life in hiding, which is not really living at all."
Then he stroked her hair again, and closes his eyes. She's precious to him beyond anything, not just because she's his sister, but more for the way she sees the world, the way she gives hope to all she touches. He'd die for her in a heart-beat. And he needs to be Zero because Zero can protect her, where Lelouch can only put her in the line of fire.
Shiki had forced his hand. He'd have to be honest with him, and be glad that he could never tell anyone else what he learned.
He sits back in the dark room and waits for the meeting. Every few minutes, he compulsively checks his watch. It's a gamble, but one he's rigged as best he can. "No weapons. No companions. Just him and me, man to man." He says, and his eyes light up. If he were honest with himself, which he so rarely is, he enjoys this beyond belief, risking it all, the world he's built and the rest of his life on nothing but his wits.
He'll miss it, when he's killed everyone who can challenge him.