The confirmation that it was working gives him a lot more confidence than what he'd gone into this with, leaning up against Yu and continuing to give little moans and noises of content.

"Yu...." he moans, his hand moving faster and faster. He adds a nuzzle or two in, pressing his head against his boyfriend in between nibbles and kisses to his ear and neck, and slips his free hand up behind Yu's head to muss his hair.