In order to cater to the needs of different players, Sine Requie Snake Eyes features four different difficulty levels, each coming with added horror and despair.
"Story Mode" is for players who simply want to enjoy story and exploration without (too many) worries: the game will give you plenty of time for each chapter and your group will find plenty of resources.
The "There is No Mercy" difficulty level will slightly reduce time and resources, while playing at the the two highest difficulties ("Only Blind Rage" and "Death at Last") will mean that a single mistake might cause a dreaded Game Over.
Difficulty is about more than just time and resources, however: the save system will be affected as well. Up to "There is No Mercy" difficulty you will be able to reload your game from the last checkpoint, while "Only Blind Rage" will force you to go back to the beginning of the current chapter, and "Death at Last" will pull no punches, forcing you to restart the game from its very beginning.