For a long while there was just the sounds of wheezes, with not a single word spoken. Hibiki patiently waited, hoping that eventually Tristan would get used to his presence enough for the panic to ease. In the meanwhile he took out the cufflink, and glanced over to see the other half still in place.
At least this is solved… 

A sudden stir from Tristan in his direction startled him slightly. Until he released that he was handing his phone back to him. The gesture made him smile slightly, glad to see a sign of goodwill, even though he was still hiding his face.
As he took his phone back, he exchanged it with the cufflink, as if to trade good intentions. Tristan took it, but it didn't appear to improve the situation much. Instead his breaths got faster and pained again. Afraid he had upset him, or that the situation was otherwise getting worse, Hibiki typed out his question. Careful not to scare him further, he held the message up. He had to guess a spot from where Tristan could see, having to lean in closer.

‘Are you okay?’

No response. Just those strained, wheezing breaths. It caused his concern to grow, and unsure what else to do he chose to go with his instinct instead. Careful not to be sudden and unexpected, he ran his hand over Tristan's shoulder. It was slightly uncanny, trying to find the balance between assertive and comforting, while he could feel the tenseness and fright. At least at first, but as he continued he could feel him calm slightly, the intensity slowly wearing off.
With one hand he typed his follow-up response, trying to explain his position in this ordeal, so Tristan could understand.

‘If you don’t want me to stay, I get it. I know that it’s scary and embarrassing to lose control over your own body, and you don’t want anyone to see. But I can’t leave you struggling for breath in a toilet stall. So I’m going to stay here at least until you can breathe again, okay?’

He was answered with nothing more than a nod, but that was enough to make him smile slightly again. With renewed confidence he continued to give Tristan's shoulder soft and rhythmic squeezes, wordlessly saying it would be fine.

At that point it was a waiting game, and it left him with plenty of time to think of what to say or do until Tristan had caught his breath again. Bit by bit he felt his breaths get deeper again, even if he sounded sore and exhausted. He still shared in the relief, now that the worst appeared to be over.
A sudden glance up from Tristan caught him slightly off guard, even if he had had the time to prepare himself for it. His eyelids were red and puffy, in rather stark contrast with the light grey of his eyes. Hibiki noticed the small scar on his cheekbone, which he assumed to be from an accident some time ago. Aside from that he looked understandably tired and winded.
On the stage, the confidence and spotlights had covered all the blemishes that made him human, but like this it was nearly confrontational how normal Tristan was. It was an odd feeling to realise that his earlier daydreams had been for the most part a fiction he had tacked onto someone who simply happened to be pretty.
Still he refused to let that get to him, if anything he was only more curious now. So he smiled and waved, hoping to meet the person in front of him, not the one he'd chased in a daydream.

‘By the way, my name is Hibiki Yukimura, nice to meet you.’

He smiled wider in an attempt to make Tristan feel at ease, despite all the unfortunate surroundings.