I'm pretty sure that's not Reiri on the left; she looks like the main character's sister, Sawawa. there are no other pictures of her here, so the mistake would be easy to make, if there is one.
no it's not, thats Sawawa. her bust size should have been a dead give away in it's own right. plus her hair is brown not black, it's not really an easy mistake when you think about it.