When is it OK to take a naked hot spring bath with your Japanese girlfriend/boyfriend?

So if you’re in a romantic relationship here, sooner or later you and your partner will probably be heading out to an onsen (as hot springs are called in Japanese) together.

But the question then becomes whether you’ll be in the onsen together. While the vast majority of hot spring bathing facilities in Japan are gender-segregated, a few still have konyoku baths, where men and women soak together. Konyoku hot springs are mainly found in especially remote rural areas, but what just about every moderate-sized or larger hot spring in Japan has are kashikiri baths, which you rent out for an additional fee for just you and your companion’s private use.

To be clear, kashikiri baths aren’t love hotel rooms, and doing the deed while in the water is a strictly prohibited faux pas. But even if your hands and hips aren’t supposed to be busy, your eyes most likely will be, since in Japan you go into the hot spring naked. Even if you’ve been on a few dates, sharing a cozy-dimension tub for 30 minutes with no clothes on is its own unique sort of intimacy, so at what point in the relationship is it acceptable to say “Hey, let’s hop in the hot spring together?”