Ria decides to visit Kyou on her own for a more serious reason while Kirino is still in the US and she would ask for Kyou's help with something involving Kirino (at Kirino's request).
Maybe she is not the same, or is not training correctly or is all sad and stuff.
This will replace Kirino messaging Kyou, but more later on when Kyou and Ruri are already dating.
Ria will not immediately say this though, and just claim she wanted to see Kirino's home country.
Kyou reluctantly agrees to be her "tour guide" at the request of Kirino and his mother and asks Ruri to help out.
One day they take her to Akihabara, where Ruri tries to show her all the things she likes (mainly Maschera related things); Ria doesn't find it that interesting and gets distracted by Meruru on the big screens.
Another day, they take Ria to the pool and while she is swimming like a pro, Kyou is helping teach a nervous Ruri how to swim.
At one point, Ria steals Ruri's bikini top and runs around with it; Kyou is torn between helping hide his girlfriend from prying eyes and trying to get her top back from Ria.
Kyou go visit Kirino, but take Ruri with him, so when they get there, we could have a pretty dramatic fight involving Ruri and Kirino.