This made Chiaki use his last leap in that time line to go back in time to save her, which in turn is why he's there when she stumbles onto the time travel device; running out of leaps made him finally sit down and figure out where he lost it so he can recharge. Later in the movie he's not there when she goes back to figure out who startled her because during her time leaping she's gone to the past before that day before, wiping out the version of him who ran out of leaps so he still had one left and didn't need to go find it. This is a very lucky break for Kousuke and Kaho.