Heard you’re lacking ideas right? Well I have some but don’t know if I should say it. Just in case, you plan on having mermaids in your thing? Cuz finding an underground secret tunnel in the onsee (I dunno how to spell it, English not my first language )if you go there enough, or you can let a shy insecure girl run the onsen and if you help her get out of her insecurity (grow bigger) she’ll show you the secret. Just an idea though, hope I don’t sound dumb