Might be a tad obvious for me to mention, but Reddit, a social media site which does allow NSFW content may be a place to advertise. A 'subreddit' that is called r/lewdgames could be a place in which you could advertise the game.
Oh, we are advertising there already. r/lewdgames is definitely the subreddit that showed us the best results. Most other subreddits - not so much. I think that's because we are not really "lewd-forward". We also have decent promotion engagement on r/magichentai and r/erogev . Most other that I tried were badly received one way or the other. But thank you for your suggestion. Do share if you can think of any other subreddits that might be a good fit for our game. It is greatly appreciated!