The hot-white and throbbing pleasure of getting his dick engulfed in her warm mouth was immense. While it wasn't a second pussy to him, the sensations it offered was still worth getting hard and excited about even while he sucked and teased her sister's nipples.
But while he was enjoying all of the sudden attention and was getting worked up into ejaculating to release his seed—he wanted to offer some sexual relief to both of them at the same time.
Whether that also turned him on even further was another thing entirely. He gently reached one of his hands out in an attempt to pull the twin over and reach her head. It was a little difficult to reach while he was sucking Rei's nipple so he temporarily popped the nipple out of his mouth and blew some air over it once.
Then finally he looked back at Kei and cleared his throat to get her attention. "If you can face your butt in this direction—"
