Thread:BleedingUranium/@comment-1784397-20130621031203/@comment-30764484-20130627010129

Emi's is by far the easiest to get. If you choose to race her on the track, that essentially locks you into her route, though you can also get Shizune's if you made the right choices with before. Racing Emi locks you out of the other three.

Kenji's "route" ends at the end of Act 1. Instead of hanging out with whichever girl you're going to be with that playthrough, you go up to the roof and drink with Kenji, and you end up falling off.