Hardcore mode is for those who want to play a more difficult game.
You can select it after watching the ending of the game, and the changes are explained in the screenshots.
In hardcore mode, manual saves are not possible, and your game will automatically save every morning.
In addition, saving and autosaving are disabled in Hardcore mode.
The Hardcore-only save slot is located in the far right corner.
In hardcore mode, you'll see an icon in the upper right corner of the screen to let you know you're in hardcore mode.