who is this artist? the style is very distinct -- and most of the "hayase" tagged images are this artist's

It's from the game Sexfriend.

are you sure it's just from that one game? do you know of the specific artist? because i have seen plenty of other characters done in this same style
a girl in the gym outfit with her panties down pictured from behind is the one that comes to mind

There might be other games by the same artist, but I'm positive this picture is from Sexfriend, at least.
The game has a ton of pictures... I think the CG set is over 100 megs.

comment #8619
They cheat though. Every pose has three or four layers of clothes/money shot.