Ah, Sumire... I once wrote that if I was in Sou's place then I would never touch my family.
That statement is rock-solid for Akane and Sakura. But I also wrote that Sumire is a different beast. She's my nightmare and I'm unsure if I'd be able to kick her out like Sou did here. If she appeared in my room, dressed like that, that's a trial by fire for someone who loves "Yamato Nadeshiko" girls.
You nailed her appearance with the work you put in this chapter. Excellent job.
And yes, Sumire, like the Konno sisters, can be viewed as a Yamato Nadeshiko - just while the Twins represent the classic beauty in appearance and regular behavior, Sumire is anything but. She has the stunning looks but her sloppy attitude and lewd personality are a complete opposite of what you'd call a lady. Aya and Hana are no better behind closed doors, but they put up a facade with Sou - and with others both are highly skilled professionals and hard workers.
Sumire is human trash, at least at home, but her redeeming points are surprisingly tied to that. She's not a closet pervert, with her Sou would get what he sees - she more or less openly lusts after him, which makes her so refreshing. But she is not unhinged and if Sou tells her off Sumire has enough reason left to stop and even reflect. And like his mother Akane she also cares a lot about her little brother (Sumire made it possible for him to go to school). For that world she's an ideal Nee-chan.
We should whoreship Sumire for her being the way she is.
(not a typo,she'd be happy to get laid for free)