If the shared HP between Neku and his partner falls under zero, the battle is lost, displaying a "Game Over" screen, and (depending on the type of battle and acquired stickers) one or more options are displayed:
- Retry battle; no penalty.
- Retry battle on easy mode; no penalty.
- Escape from battle; Sync is lost (unless an item with the Nag-free escape ability is equipped).
- (Not possible during certain battles, such as fighting Taboo Noise).
- Return to title screen; allows you to continue the game from the last save point.
If the HP of a Noise reaches zero, the Noise disappears (from both screens, if it existed on two screens to begin with).