I see a lot of people are confused about the setting so I'll try to help, even though I'm not a novel reader. The story references the economic bubble burst a lot, which is an event that happened in Japan in 1992. Basically, Japan's economy had been rising rapidly post-WWII, which inflation rose so high that it was like a imploded bubble. When it bursted, prices dropped and everything went to shit. You can imagine that plenty of companies lost their assets or bankrupted. Rei mentioned that her father lost his money when the bubble burst, then brought her to her grandmother after that, combining with her high-school age, I'd say this manga takes place in 2000s Japan. Although you can probably guess that already, since the manga shows smartphones being used widely among the rich kids, but not cheap enough that a poor person can afford.