Some relevant things about them:
Their pairing is officially called SayaIshi, on 2ch they're already on to their 12th thread (since every thread is closed automatically at a thousand posts...you can see how popular they are
).
Riho's most recent comment about Ayumi's lips.
I think the best part was how Fukuchan said "出た!出た出た!" because it implies that it isn't the first time she heard this.
The first time we heard of it was in Morning Jogakuin, the second episode (4th April 2012), when Riho comments about Ayumi's lips in the Renai Hunter PV. Then on Riho Deli #34 she talked about how Ayumi had a very nice body because of the way her muscles were shaped (where are you looking, Sayashi-san? :3).
Also, the live audio recording of their CRAZY ABOUT YOU dance battle in the 2012 Fall Tour.
http://video.sina.com.cn/v/b/87374369-1805256214.htmlThere's a lot more stuff at this wota blog:
http://ameblo.jp/dooishi/theme1-10060987433.html for those who can read Japanese.
I thought I was observant, but this person takes the SayaIshi ship very very seriously.