Re: Shub-Niggurath [Adult]
Would this be set in the modern day, or in a more ancient Japan? The culture of the islands has changed markedly from then to now, but the underlying foundations of Japanese civilization still hold sway to a remarkable degree, almost as if the culture has incorporated the best of Japanese traditional values with the best of those ideas acquired from Western civilizations (mainly America, England, Germany, and France) over the centuries.
Would you seek to integrate Shub-Niggurath with the lores of Shinto, Buddhism, or would you make this witch-cult you mention something separate, apart, and hidden?
There is a certain inevitable resemblance between common artistic portrayals of The Goat With a Thousand Young and those so-called "tentacle monsters" prevalent as a hentai trope, so it would be wise to make a decision early on about any possible connections there.
I'd be interested in exploring this setting. I'm no expert in Japanese culture, but did experience it first hand as a child for almost eight years, and find myself still heavily influenced by it in my thinking today.
Sukoshi Nihongo dekimasu. Asobi ni iku, yo.
(I speak a little Japanese. I'm here to play.)