The games are usually standalone stories taking place in post-apocalyptic worlds with recurring themes of philosophy, religion, occultism, and science fiction.
Key elements of the gameplay include: (1) player-driven choices to place the protagonist in an ideological "alignment" (usually Law/Chaos/Neutral); (2) the recruitment and use of demons/creatures/deities/historical figures from various mythologies and folklore. Colloquially by fans and in-game they are all usually just referred to collectively as demons. Use the general Demon (Megami Tensei) tag whenever they are featured in posts.
For Danbooru purposes this tag is exclusively used for the set of mainline games and Megami Tensei is used for the overarching franchise. See that wiki for a list of spinoff series.
