The Megami Tensei franchise at large is easily best-known in the U.S. for its Persona subseries of role-playing games. But that’s just a small handful of games in a much larger franchise. The main Shin Megami Tensei series has long been known for wildly difficult, punishing gameplay, and that reputation was firmly established with the release of Nocturne, the third game in the main series.

Shin Megami Tensei: Nocturne saw its American debut 15 years ago, on October 12, 2004 for the PlayStation 2. This release was based on the “Maniax” edition of the Japanese original, which included cut content from the 2003 Japanese inaugural release, such as an optional dungeon and additional possible story ending (and, memorably, the inclusion of Dante from the Devil May Cry series as a guest character). Nocturne was the first game in the Megami Tensei franchise and the first Atlus title at large to receive an M rating from the ESRB, as Atlus went out of their way to make sure that the English localization was true to the dark and mature themes of the Japanese original and didn’t want to do anything to dumb it down, saying that doing so would have been “a disservice.”

Nocturne is set in Tokyo before and then during an event known as the Conception, where the world is destroyed by the actions of a cult that wants to prevent the world’s total stagnation and instead wants it to be dictated by the Great Will. The protagonist begins as a human, but is contacted by Lucifer and infused with a Magatama that turns him into a being known as the Demi-fiend – an entity with the heart of a human but the powers of a demon. The Demi-fiend is tasked with exploring the world post-Conception – now known as the Vortex World – which has two cults vying for power in order to remake reality for themselves. These cults are the Assembly of Nihilo, led by Hikawa, and the Mantra Army.

The Demi-fiend’s actions in the game lead him to face off against both groups, but ultimately it is up to the Demi-fiend himself to choose how the world will end up. He may choose to support one cult over another, leading the world to be reborn as they like it – or, he can choose to go his own way, supporting Lucifer himself and breaking the Great Will’s control over the world and its cycle of rebirth.

Nocturne used the turn-based gameplay typical of Atlus role-playing games, with battles making use of the Press Turn system; the battle has every character starting off with one Press Turn, and any action making use of it. However, doing things like scoring a critical hit or exploiting an elemental weakness can grant an additional turn, allowing them to create devastating combo attacks before their opponent can make a move. This can be done both by the protagonist and against them, and the enemy AI making use of such a system gave Nocturne a far more strategic element to it.

The game saw significant praise upon release, with many considering it to be one of the best role-playing games of its generation even despite the ruthless difficulty that can present itself. Nocturne sold well worldwide especially for an Atlus title, and its success helped further the awareness of the Shin Megami Tensei franchise in English-speaking companies – which, in turn, has helped to make more recent titles like Persona 5 massive mainstream successes.