Riku's head was still lowered to try to look at her. There was a slight edge to his voice, but considering what he'd just been told, who wouldn't? "Last I checked, the only time Roxas would have a girl's voice is if he got hit below the belt. Was Vexen having an off day? 'Cause if I didn't know better, you have someone else's voice." That doesn't look like Roxas's nose, either. I don't know... Riku never did study Roxas's face. That being said, despite Xion's build and in addition to the voice, something about the individual felt female and didn't match up to what few visual cues he was getting.