I was like... did I miss a chapter? when I first read the first page of this chapter. It's just a flashback of Kyoko's, correct? Now with what happened recently, Kyoko's suspecting his past.
Ren is using the smile to hide what happened to him now.
It's weird that it's Yashiro worrying about the number Kyoko given to Kijima instead of Ren (who probably is hiding his emotion behind the smile), until seeing Kyoko's reply with color messages.
It's been a while since Shou showed up, and he's going to school (he's still enrolled?).