Secret bath customs, huh. You'd think it'd be normal customs in the Hentai world.
Also, I suppose this is why you don't just randomly answer 'yes' to a question you don't understand. Still, how nice that they actually understood enough english to tell her all about the...custom at Japanese hot springs.
Great ending though. Well hey, I'm sure those guys and their friends would be happy to welcome her friend into the mix, maybe teach her a bit about these 'customs' as well...
Wonderful , Fabulous! Gangbangs are my favorite, and she's cute! The only thing I would change, is to have her be somewhat older, maybe a wife? Who was allowed to sneak off to explore a hot spring, maybe while her husb golfs or something? Not exactly NTR, but sharing her body with many strangers is exciting too! :)
Chances are the 'secret' to the hot spring is connected to understanding what was posted on that sign. But it seems the only way to get the understanding is if the artist produces a sequel story. To Puyocha-sensei: "Make It So! Do Not Resist ... It Is Your Destiny!"
We opted to leave the sign untranslated to fit with her monologue on page 3 where she's unable to discern what's written on it.
That said, there's nothing really relevant to the plot other than the fact that it's a mixed open-air bath. It contains the name of the hot spring, the location, as well as the contents(Magnesium Bicarbonate), temperature(40 celcius), and specifying that it's a natural formation with no extra additives. In other words, you're not missing any secret wink-wink, nudge-nudge as if the sign says "orgy bath" or something.