Shin Megami Tensei: 20XX

Shin Megami Tensei: 20XX is a 2004 role-playing video game developed and published by Atlus. It is part of their Megami Tensei series, and is a prequel to the 1994 game Shin Megami Tensei II, taking place decades earlier. It was released for Japanese feature phones starting in 2004, and was re-released by G-Mode for Nintendo Switch and Windows in 2025. It was followed by the spin-off Shin Megami Tensei: Devil Colosseum 20XX in 2007.

The game follows a boy in the Valhalla district of Tokyo Millennium, who is helped by a man to gain strength in exchange for helping him take down the woman in charge of the district. The player takes the role of the boy and a girl accompanying him, and navigates dungeons in a first-person perspective while fighting and negotiating with demons. The game was well received for its branching story and the complexity of its demon fusion mechanics, and was a success, with 100,000 downloads as of 2007.