Correct; there is almost always a second-person charge in Japan. Also many European hotels.
At ICH hotels, the "double occupancy at single room rate" benefit eliminates these charges for Ambassador and Royal Ambassador members.
But it doesn't eliminate them for CP and HI hotels, sadly. And I don't believe that there is a Spire benefit to eliminate those charges. It would be nice if they did.
I have found in many cases hotels have waived the charge, but recently had this very discussion with the CP in Kyoto.