Shin Megami Tensei: 20XX is a Japanese cellphone game, created as a sequel to Shin Megami Tensei, showing what would have happened if the Order of Messiah won. There was a prequel named Shin Megami Tensei: 20XX Devil's Colosseum.
The gameplay and music are taken from Shin Megami Tensei II and Shin Megami Tensei: if.... 20XX has a harder difficulty setting than its predecessors, the Virtual Battler, and a new enhancement known as "Elemental Based-Stats" (which grants an element to the demons and a weakness).
During the year 199X, the sudden appearance of a large number of demons threw Tokyo into a state of chaos. Seeing this, the ambassador of the United States of America, Thorman, initiated an ICBM strike intended to wipe out the demons in one fell sweep, which caused the destruction of Tokyo in the process. 30 years later, with the completion of the Order of Messiah's Cathedral, the Messian's victory was finally guaranteed. At the end of the conflict, those who survived were gathered as one within the Cathedral, and after many decades, what was once known as Tokyo came to be reinvented as "Tokyo Millennium".
It's here that one day, living in the slums of Valhalla, a young delinquent received a COMP from a strange man...
- The Hero: The 'other self' of the player, who lives in the slums of the Valhalla area. He has no memory of his childhood, and so his only desire is to become stronger, spending all of his time honing his strength through street fights. Since receiving the Devil Summoning Program on his COMP, he's taken to polishing his skills at the Gym. His appearance is unknown, though his trainer says he's "well-trained, but lucky enough to have some extra meat on his body."
- Ain: A dark-skinned lady suffering from amnesia. A former resident of Valhalla's underground area, it was a matter of chance that she met the protagonist. Is capable of using Zio and Dia magic. It can be said she has a fundamentally polite and well-behaved personality... An event that occurred when she was young will make the tragedy that befell the protagonist become apparent.
- Moss: Friend of the protagonist. A young boy with a plump physique who prefers to dress in green. Because he wants to become stronger, he introduced the mysterious man to the protagonist.
- Trainer: A muscular man and head of the Gym who took up the role of being the protagonist's guardian. His voice can be blunt, but he's still kind. He doesn't like the idea of his boss also being the owner of the gym.
- Owner: The owner of Valhalla's gym. A man who likes to wear sunglasses. He's a bit smug, but still well-known.
- Haneda: A man in his prime who made his initial appearance in Shin Megami Tensei II as the owner of the Haneda Gym. Fighting under the nickname 'Feather Adonis,' he amassed a large fortune at a great speed. He confronts the protagonist at the end of the final confrontation in the coliseum. He used to be far more arrogant, but his voice is still haughty and gives off a narcissistic impression.
- Okamoto: A man in his prime who made his initial appearance in Shin Megami Tensei II. He's a masculine man who once used the nickname 'Kira-tsune'. He confronts the protagonist at the end of the final confrontation in the coliseum.
- Madam: The manager of the Valhalla area who made her first appearance in Shin Megami Tensei II. She is naturally knowledgeable about Valhalla, but possesses knowledge about the news within Millennium as well. She permits those who reign victorious in the coliseum access to her mansion. She seems to know about the protagonist and Ain, and the important task that they are to undertake throughout the story.
- Ramedo: A combatant of the Messians who's a little bit arrogant. After becoming a Temple Knight, he swore allegiance to God, but...
- Founder Metatron: The commander assigned to hunting down and executing the result of the Gaian's project, Ain. He seems to have an interest in the project for some reason...
- Lord Mara: The one in charge of the Gaians and their project. According to the Demon Lord Lucifer, they ate the Messian's forbidden fruit.