I really appreciate when an author can actually pull off having a third character join in and they not feel like a third wheel. These chapters have been nice. I hope we get to have more with Ranbara later.
That's because Ranbara is not a meddlesome and insecure interloper, but immediately recognizes that the other are a couple in all but name, finds a realistic spot for herself in their arrangement at a comfortable distance (a friend of both partners), and offers up her resources (the bathhouse fee) upfront and without strings attached to show her sincerity.