Chapter 2 on MD I never doubt Kodama to add more dark backstories to all characters because she feel like having happy characters is no good for a manga. MC is a coward and can't even bring to get respected by middleschooler. Manager is just there, can't say anything since you barely see her and when you do she just doesn't care. And last, we have the 3rd girl, the grow up one, Kodama in her extreme generosity decide to give her the twisted family, she is the daughter of her dad and his mistress but the mom is kind enough to let her live with them and the other daughter, who is one of her classmate. Said mistress is suposs to bea prostitute btw because why not and when Ashima get back in the end of the chapter, she kiss her "sister" because of the bad mouthing her "sister and her friends have done to her. Oh and she get bullied too but she doesn't seem to care one bit.
So yeah, it's really a Kodama manga.