Hey, the fantasy mode is enabled automatically when you apply a certain body feature (that you have already unlocked); currently, there are two such features that are given as a reward for one of the endings. You cannot trigger it manually; its main purpose is to limit interactions (like performing in the club) while you have these body features applied.
By X, do you mean that the heart is 'broken'? If so, you can get it back when you match the preferences listed on the Affairs screen. The game is designed to have body changes back and forth, so it is expected that characters will stop liking Ryoichi at some point, and then start liking him again when his looks match their preferences.