Ianto chewed his lip, a bit embarrassed that he'd asked in the first place, but at the same time...he really wanted to know what the answer was, anyway. At Sulu's question as to why he asked, it was Ianto's turn to shrug, although he did go on to explain himself. "It's just... I mean. I was talking to Merlin, earlier today, and. He calls you Hikaru. He asked me why I didn't, when I'm obviously pretty close to you and all, and...I didn't know what to say. I. You've never told me to refer to anything other than Sulu, so I just assumed. But then, he calls you it. And well. I saw Jim and Dr. McCoy using it a few times on their posts, so. I..."

Ianto trailed off, even more embarrassed than before. "I mean. It is your first name. I... I think it's pretty safe to say that we're close enough to each other for me to call you it, and yet. I... I don't. I... I don't even really think of you as, y'know, as 'Hikaru'. But. Merlin started asking those questions, and well. I...I started wondering if maybe I should. I don't know." He ducked his head further against his chest, so that hopefully Sulu wouldn't be able to catch the magnificent blush that was spreading across his face quite so easily, though honestly, it was probably a lost cause.