Before Your Memory Fades

The first two books made me cry but this just didn't hit.

I thought we were working with the concept of “you can't change the present by going to the past” because anything you do has already happened, but before Reiji goes back, Saki (I think) tells him Nanako's answer to the last question was option 2 (and is emphasized as further motivation for him to go!) but when he's there she says option 1??? It didn't seem like Saki lied, so did Reiji change time? What happened there?

Also, the pee off a frogs face line is having me contact my Japanese friend for fact checking because what the actual fuck.