This is not the ninth Shin Megami Tensei game; "nine" is the number of character attributes and alignments used in the game: Law, Chaos, Light, Dark, Neutral, and their variants. The game is set in the future. Tokyo, Japan's capital, was destroyed in a nuclear explosion early in the 21th century. But some years later the Tokyo of the nineties was digitally recreated. People live in a virtual world, and everything is ruled by computer programs. But some programs don't work correctly, and one day, a pop concert is disrupted by a terrible demonic vision. A special agency recruits the hero of the game, Kei (which can be either female or male, depending on your choice), to travel through the virtual world and to confront the hackers who might pull the strings behind the scene.
Like in all Megaten games, demon summoning plays an important part in "Nine". You can have several parties, up to eight characters each, and form them at your wish from the demons you manage to recruit. Talking to enemies is even more important now, as you get experience points from equipping items and not from battles. You can also fuse demons to get more powerful ones. The battles are now in real time, both parties attack simultaneously, and precise timing is required. In addition, some portions of the game are occupied by virtual battles between hackers, which resemble a strategy board game.