@mage_goo So much this, I was about to comment on the same thing after reading this and past weeks chapter. I mean, why couldn't Chizuru do with a bit of normalcy within her life? She already seems to be too perfect to be a good combination/to complement the MC. She was already stated to be pretty, intelligent, self-sufficient, independent and you go and top it off with a tragic background as well. I mean, her grandma is already dying, but now you say her parents are dead as well (one of them at least)? Last weeks chapter and cliffhanger made it seemed that Chizuru was by chance a Wayne.
@Sh4dey I don't think that Mami is a case of a childhood-love revenge story with Kazuya. It was mentioned ages ago (backhandedly), that Mami was to be married off with a businessman/associate/friend of her parents, so in response I think that Mami decided to date someone, to keep her parents off of her back, and what better subject than the thirsty and horny MC, Kazuya. After a while, I believe Mami decided to let go of Kazuya since the guy had already served their purpose (fending off marriage arrangement) and since she knew she was considered a pretty girl by many, with a somewhat rich background she went to search for others guys to date. All of that went spiralling down after a while with her unsuccessful dates (apparently she got bored of the guys she dated) and when a few days later Kazuya appeared with Chizuru, it only served to unleash her insecurities about herself, becoming possessive and jealous of the relationship between Kazuya and Chizuru, which at the same time irritated her because it made it seem Kazuya had gotten over her, pretty quickly and moved on to a better girl.