Start with a standard Isekai setup. The main character gets hit by a truck, briefly goes to heaven and is assigned an exotic new life. In this case the main character (MC) is a NEET who has gone through 850 reincarnations without doing anything good or bad enough to change his karma. At this rate (says the god / goddess lecturing MC) he will certainly be lost in the Kali Yuga (Hindu/Buddhist end of the world) and other humans are acting the same way in increasing numbers. Better that all of humanity goes to hell than permanently die of okayishness! So as an experiment he will be reborn into an Earth defined by a combination of his favourite anime genres to force him into doing something interesting. For example a world defined by magical girl / harem romance / hentai would have a population of cute witches fighting over the small number of men available for sex.
sounds like it'd be similar to the fetish public story where you get any 2 fetishes to alter the world. Would end up being a "fat" story in the sense that you'll end up with many starting branches that don't get that deep. Interesting idea though.
One on hand I get annoyed with "fat" stories as well. On the other hand finding out what combinations others come up, even if they don't go anywhere, would be fun. I came up with this after getting frustrated with the comparatively high-bar I set myself for detail and realism in another story. That one is a lot of intellectual fun but I knocking out something based on a bunch of chliches might help my writing speed.
