It exists without the girls, look at the pokemon franchise, But what about the girls?
Pokémon isn't a gacha game though, It's a creature collecting game. They are quite different.
Gacha mechanics are something like Japanese version of lootboxes. But instead of skins like usual, you get characters, and sometimes also weapons(or something else gameplay altering) for them. They come in "banners" pools of characters with completely random chance of who exactly you gonna get or time-limited ones with high chance of getting someone specific.
Each pull from the gacha require you to spend an ingame currency. If you ever played Pokémon, that is not how it works there at all.
If you are interested in creature collecting games,
https://f95zone.to/threads/pokemon-like-adult-rpg.49135/ Maybe this thread may have something of interest. Can't give any personal recommendations, i haven't found a game in this genre that would really catch my interest.
As for actual gacha games, i would even be happy with non-offline one with actual hentai. But there are none i know of.
I'm also not sure how 100% offline gacha game should work, since it's made to be a live service.
Constantly updating banners with new characters, constant addition of new story content and also events.
A lot of enjoyment from gacha games, at least for me comes from ingame currency management and planning for the future, do i roll for a waifu now, or save and roll a more meta waifu, or save currency till next time a character i want is on a banner and i have more chances of getting them, e.t.c. whole game is like a single run in a roguelike game, but years long. Also i'm all for playing this types of games as F2P, it's actually more enjoyable this way. And you also don't have to give your money to greedy devs using their vile manipulative monetization tactics of course.
