Hoshi no Ponko to Toufuya Reiko

星のポン子と豆腐屋れい子

Reiko and her little brother find a weird creature that looks like a cat with wings, and they sneak it home with them. To their surprise, the creature explains that it's an alien salesman, here to trade advanced technology for something called "hahise," which is abundant on Earth. Reiko and her brother are tempted by a device that can duplicate anything, even money. When they make that half-understood deal, the course of Reiko's life is shifted in a much darker direction... (Source: MangaHelpers)