Fiends are powerful demons present in each Shin Megami Tensei title. They have no direct bearing on the plot, but are merely difficult battles used to challenge the player. In the original SMT, as well as its sequel, the chance of meeting these Friends was 1 in 256. They appeared in specific areas only and defeating them would leave your party with some very powerful equipment. Such Fiends were not even covered in strategy guides, allowing for a lot of rumors and talk concerning the Fiends true locations.

Fiends were added to the Maniacs version of Shin Megami Tensei III in Japan. They are all present in the US version of the game, which is based on the Maniacs version. These mostly include the skeletal figures after the Candelabra. Each of these Fiends is based off one that appeared in the previous two SMT titles. However, the battles are nowhere near as difficult (although they are still challenging), they are not difficult to come across and the only resulting items are Candelabra required to open new Kalpas in the Labyrinth of Amala. Two of the Fiend battles are required to advance the game, the rest are optional.

The main character in SMT:N is refered to as a "Fiend" in the Status menu before enough Magatama are mastered to determine his race. Dante is also called a Fiend within the game.

Codeword used by Karma Society troops to refer to humans incapable of transformation.