Listen to the Rain

My understanding is that it's the transition between source material. The first part is the adaptation of one of the light novels and the second part is a different novel, which leads to different themes.

I've also heard it's because Kawahara isn't a great writer and leapt to otaku tropes when he hit fame and moved beyond writing a keitai shōsetsu, but I've never actually read his writing so I can't confirm that.