It seems as though Ruriko cares for Rio more than I expected...
Also, Ruriko was always a huge softie, so this development definitely makes sense.
I'm looking forward to seeing where things go. The message from Rio at least had some sense of urgency to it, so while I'm expecting some sort of a red herring, it might not be. Besides, simply her existence has already accelerated the moving of the gears on Kurumi's side, which is great to see. The hug was adorable.
This is why I'm also not fully agreeing with some of the comments that mention how things developed "smoothly" or "naturally" till now. I mean, at least I don't feel that these developments are either manufactured/contrived or particularly bumpy. There was a significant part of Ruriko's life that was fully separate from Kurumi (and vice versa, obviously), it was bound to come into play at some point.
Heh, it would certainly be interesting to see Rio, as ignorant as she is of the exact circumstances of their marriage, happily talk to Kurumi about how glad she is that Ruriko finally got to marry her after pining all those years. :D
Also this. I need this. Need.