This isn't too difficult to get and you can get it early on if you don't send any money to the orphanage in the early game. You can get this in Act 1 playing as Kiryu with the hostess Riku as your date. All you need to do is keep her "love" meter maxed out for the first bar and ask her on a date, even on meeting her the first time. Finish the session favorably and as soon as you exit you'll be able to go on a date with her. If you're just achievement hunting, just revert to your last save, but with all of the hostesses, they all have their own hidden substories so it's up to you if you want to revert or not.