Tristian was preparing to cut Yasu off, not really about to stand him degrading his and Ren's relationship as similar to playing with new toys, when someone else interrupted. He stopped, mouth partially opened and turned to look at Ren, clearly broadcasting that he was quite unsure what to make of what was happening. He mouth "Who is this woman?" because he'd certainly never seen her before, nor had he ever heard Yasu ever sound so, dare he say, soft? It was definitely out of the realm of what he'd considered possible for the other designer.