Upon winning a game in one way or another, the player is given an option to start a New Game+ (or New Game Plus). The option is only available for a day on which the player won, displayed as a button to the left of the screen at Home. Starting a New Game+ (frequently shortened to NG) allows the player to use their Main Character and five team members for a separate, new run of the main game. The NG provides additional challenges, however.
When the player sees the score screen upon victory, a NG button will appear to the left side of the Home screen. Clicking the button starts a New Game+ immediately, taking your Main Character and five team members currently in the party. All equipment currently on will be preserved and transported, but the storage will refresh and almost entirely vanish. Resources such as money and stone also reset. Of note is the removal of home upgrades. A player who chose the Established trait at the start of the previous game may notice that the passive income has disappeared, as all home upgrades are reset upon a NG.
Relationships with Town NPCs are also reset and, to recruit them and to make their associated home upgrades, the player will need to get close to them again.
The party that the player started a New Game+ with will have disbanded and they will be the only characters at home.
The effects of a New Game+ can be seen early with the cheat code "newgameplus". This disables achievements and unlockables as cheat codes always do.
The world receives global effects upon each new NG. Some affect the money cost of everything in that world, while others grant a random combat buff to all enemies at the start of every fight. Further, the hostility rating of everything increases per NG. If the player reached a NG while in freeplay, the World Level will be retained and then increased. Finally, enemies receive a straight boost to their stats, regardless of how minor.
Effects less openly hostile to the daring player include increases to stat limits. The Main Character will receive a 5 increase to their level cap. Limits for genes get relaxed globally, and as such a player with means to manipulate the team's genes can empower them with each iteration.
For the daring player, the reward is another opportunity to challenge the Achievements. With the NG, Achievements that require early difficult action can become trivial. Those that require certain conditions to be avoided at all can be more easily managed.
The New Game+ option is still available in a NG itself. In this case, the world enters a New Game++. Each iteration adds a plus sign to the game, each time compounding the increased difficulty and effects of a NG.
Distinct NG effects appear to peak at New Game++++ (with four plus signs). With the fifth New Game+, the world will receive numerical boosts only. The point at which the plus signs cease to add has not been observed yet and may in fact repeat infinitely.