We are 3 adult women (of various ages) traveling together in Japan for 2 weeks. We will be visiting Tokyo, Osaka, Kyoto and maybe 1 or 2 small towns. We would like to have all 3 adults share a hotel room since none of us wishes to room alone. Any ideas since most hotels we have looked at online permit only 2 adults per room?

Stay in hotels with "Japanese-style" rooms. These have futon beds and charge per person, so adding in another person is usually no problem.

We are headed there on Sunday. My husband and I and adult daughter. In Kyoto staying at Kyoto Brighton Hotel which has some triples. In Tokyo staying at Four Seasons which was no problem to book with a rollaway.
Honestly, when looking it did not seem difficult, sometimes you just need to contact hotel directly via email as may not show up on website.

Thank you so much for your help - I will look into those options -

>> ... with a rollaway.
or maybe a futon. or a futon on top of the rollaway.

Just came back last week. the two hotels I mentioned had rollaway beds. the two ryokans we stayed in had futon beds, but that was all for all three of us. We had no problem sleeping on the futons.

Welcome back, jgg.