Start slowly, but not too much.

Natsu knew that, when it came to sex, it was usually better to take things slowly, but he also didn't want to waste much time, they were supposed to be on a mission after all. "Full Mast." he said, and he was immediately able to see how aptly named that trigger was, as Grey's uncovered member quickly grew and stiffened. "Ah!" Grey complained as his hard-on started to become painful. "I'm sorry, Natsu, I don't know what's gotten into me. This has never happened before, what can I do?"

Natsu observed Grey as he looked around failing to find a way to find release. He didn't try anything with his hands, apparently, the trigger's effect meant he couldn't even conceive touching himself. Natsu was sure if he kept that up he could get Grey to ask him for help with that, but it was not the moment, not yet. "Maybe you should try a more Hands-On solution..."

Almost immediately, Grey's right hand was caressing his dick. It seemed he had also decided to start with the slow and soft approach, since despite how hard he was his movement did not go beyond a gentle stroke. "Ah, I'm so sorry about this." Grey said, as his face got redder by the second. How he still had enough blood outside of his cock to make him blush was a mystery to Natsu, but he didn't dwell on it too much, his gaze captured once more by the hand softly moving up and down said throbbing dick. "Please don't look, it's embarrassing." Grey said, biting his left finger trying to contain a moan. How could an ice mage be so hot?

"Don't worry about me," said Natsu, "It looks like you need help, but I can't help you with my eyes closed. Here, why don't you try sitting here?" Natsu took off his vest and extended it over the ice table Grey had made earlier. The ice mage could probably stand the cold no problem, it'd be no different to him than a regular wooden table, but Natsu didn't hesitate to take the excuse to start undressing himself as well (not that he needed one). Plus, the softness of the fabric was probably nicer to sit on. Grey did as instructed, and he started gradually pumping his dick harder as he got more and more turned on, and more and more frustrated about finding himself unable to cum, no matter how close he got to the edge.

"Natsu, I can't... ugh! I can't finish!" He said in between grunts. It was time for the next step.