You need to reach the end with all five hearts in order to unlock all three options at the end. (EDIT: Apparently this isn't the case, you just need to see the other endings to unlock the true end. Enjoy the walkthrough anyway lol.) Lost hearts persist across saves; reloading after a game over will give you enough hearts to continue, but won't refill them completely. You can only restore all five hearts by starting over from the beginning. (However, I believe that once you unlock all the endings, the choices will stay unlocked in future playthroughs even if you don't have five hearts.)

Choices are abbreviated to avoid spoilers. Other than choices with hearts and specific choices marked in bold below, you can make any choices you want. There are only small variations, but you're free to save & reload to see them.

• Every time S...
  
• Me
  
• A user, fuel...
  
• Start a new game
  
• Dissuade Luna...
  
• 2 people
  
• Cannot be done
  
• My death...
  
• Denes
  
• Save, then choose Stop...
  
• Start a new game and don't click Exit when the option appears
  
• Load the save and choose Continue...
  
• Someone was...
  
• The user...
  
• Cecilia

Who can put an end to everything, and save everyone?

1. Luna->End 1
   
2. Cecilia->End 2
   
3. Myself->End 0

(The third option will not appear until you've seen the other two endings.)

Losing all your hearts will give you a game over. There are four different game over screens which appear randomly.

Note that since making an incorrect choice will remove that option from the list, you can only purposely kill yourself on choices with three or more options, unless you've purposely gotten yourself down to one heart before. (But since there aren't unique game overs for each choice, there's really no reason to do that.)

The choice with the correct answer "A user, fuel..." seems to be bugged and will give you a game over if you get an incorrect answer with 2 lives left.

Guessing S's identity wrong will take all your lives.