Not a dev, but been in the community for a decade at this point. So, take my advice for whatever its worth.
First of all, don't chase trends. Especially not if you're looking to make this anything other than a hobby. This community is hypocritical by nature. Everyone is constantly searching for something new, yet many of us stick to the same niche. While joining a specific niche may be helpful in the short term, just ask how could/would you compete with the games already successful in those categories? Those games already have a substantial amount of content and continue to add more. What are the chances that you'll create something they haven't, and never will create?
So, just do your own thing. Despite the fact that this community has continued to grow (although, that growth feels stagnated lately...), we are still a hobbyist community at the end of the day. Just like the rest of mainstream culture, we've gradually become more toxic overtime. Trying to force themselves to make content they don't love has caused numerous developers to flee, never to be seen again.
Additionally, temper your expectations. As I said, we're a hobbyist community. Chances of a developer being able to do this full time is limited. Most of the highly successful devs have been doing this for years. They've either already have a record of completed games, or have had highly popular games in development for years.
BUT, if you REALLY want to follow trends for whatever reason, the first advice I can give is look outside of this community. Anime, Manga, Hentai and mainstream media have been a source of inspiration to developers since this community was founded. Good examples could be the manhua/manhwa scene. The manhwa scene in particular is rapidly increasing. Plus, Korean culture as a whole is simply getting more popular. I haven't seen many, if any, games exploring those themes and troupes. Could be a freebee. Dunno.
Another thought is to steal someone else's work. Checkout the abandoned games. Find one you like, with some decent levels of popularity, and create your own interpretation of it. That way, your game will start with some form of basic level of interest, giving you a head start over 99% of other new games. Just make sure you make it your own spin, not a 1:1 ripoff. Also, try to find out what was wrong with the original, and why the og dev bailed. If you repeat the same mistakes as the OG, expect significant backlash.
Just a general piece of advice, characters are your greatest asset. No matter how generic a story, with interesting and likable characters, the story will feel interesting. It doesn't matter how many times I see the same sex scenes, if I like the character, that's all that matters.
Lastly, explore AI for inspiration. Especially explore character cards such as chub. Cards are extremely simple and easy to create, which has allowed creativity to run wild over there. You should be able to find some useful character/scenario ideas over there and even find some popular trends to follow if you need it (male:female ratio worlds are extremely popular).