The thing is, it's been demonstrated that Satou is the only one who can take care of Shio. Asahi can't even take care of himself, let alone Shio, and Yuuna abandoned Shio because she realized that she couldn't take care of her either. Would Shio really be better off in a foster care system (which are always clusterfucks)?
Satou provides Shio with shelter, hot meals, baths, a bed and a roof over it, electricity, and not only that but also the genuine love and affection that Shio has been literally starving for her entire life. Satou is willing to work multiple awful jobs to do so, and does it without complaint (her only actual issue with the rapist manager was that she was docking her pay), and for someone who's also a high school student she's doing a damn good job. The fact of the matter is that Satou may have done evil things, but she not only makes Shio happy, but also takes care of her; if Satou had not found Shio, she would have been left to god-knows-what fate on the streets. What exactly is Asahi's plan if he were to reunite with Shio?
Also this is my first post after lurking for several years, hi