I think she's consoling him after a breakdown. There's only one time in the series I can imagine Keiichi breaking down like he is here, and that's right at the end of Onikakushi-hen. I guess "Believe in me" worked this time.
@ Comartemis: No you´re actually wrong Keiichi also"breaks down" in Watanagashi-hen(and Meakashi-hen) when they are searching for Rika and Satoko, he blames himself for their disappearanceés then Rena also consoles him and tells him shes not going to disappear, still it seems this pic is a "Good End" to Onikakushi-Hen