First of all you have to choose him as a training partner in tennis practice on day 1, then on day 2 you have to choose "go to the gym" to talk to Chester and Dozzer, accept the invitation to stay at the gym to train For a while, you'll have to go to the loockers and that's where you'll meet Darius and you're ready to start the great story behind one of my favorite characters, I hope you enjoy it.
sorry for the bad English