There was a browser game that I played back in 2012 which the protagonist was a high school/college transfer student, it had a lot of time-sensitive events that you had to complete to get affinity and then h-scenes with the girls (which weren't actually well drawn, if I remember well). It also had a money system with Cash and Black Diamonds (or rough diamonds, something like this) which you could buy Diamonds low and sell high to make profit, and there was also a secret ending related to these diamonds and some magical power within then.