I know that we need to type PrincessHeart in order to unlock the costume, but what do we have to do to get the game to tell you the code? When I beat the game on the first playthrough, it told that HappyBirthDay was the code for the Heather Shirt during the Game Results screen. What are the requirements in the game for it to tell me that PrincessHeart is also a code?

According to the guide you just have to finish an Extra New Game. I assume that's correct although there was at least one mistake in there and I can't remember.

I just looked at a FAQ and it said that you unlock the Transform costume at the end of an Extra New Game, but that I need to unlock the Heather Beam as well in order to unlock the Sexy Beam. Could that be what you were talking about?

Sorry, I failed to communicate my point clearly at all, I think I need sleep. What I meant was that there is at least one mistake in that guide regarding the costumes and I couldn't remember how I got the Princess Heart costume, so I wasn't sure if it was correct in this instance or not. Sounds like it is though.

I got the PrincessHeart after completing an extra new game. So PostCode is right.