Izumo is a series of eroge produced by Studio e.go!, that heavily references ancient Japanese legends and myths. While mostly developed for the Windows platform, some of the titles have been adapted for consoles (and turned into all-ages versions in the process). There are also anime adaptations of various games in the series (some h, some all-ages).
With the exception of Izumo 2 Plus, each of the game in the series are relatively independent of each other. References to key events in the prior games tend to be sufficiently explained. Of course, having played the earlier games in the series will greatly increase the enjoyment, as you'll understand more of the references.
Games in publication order