Honestly it *feels* like an NTR at first but really re-reading it, it looks more like this could be a normal, semi-vanilla story about a girl doing pervy streaming except for two things: 1) Mao looks like a typical NTR antagonist and 2) lil bro catches on to his sister's sex streams and needs to be told off. She pretty much does everything totally consensually and at worst is just engaging in some poor judgement because she was wrecked emotionally by a bad breakup she talks about on pg11.
Oh yeah and the art style also helps the NTR vibes too.
Nah, he can have his reasons but treating people poorly still makes him an ass, especially if she doesn't know why he's being like that. From our narrative perspective we can see his thoughts and go "ok he was abused and has sympathetic reasons for being this way" but until he opens up there's no way of anybody without that viewpoint of knowing that. In any case being swept up in and perpetuating the cycle of abuse still makes him abusive. Considering she's a runaway and makes several vague references to coming from a poor situation it's possible her home was a similarly abusive or neglectful place, yet due to our limited information we can only guess, much like she's shown suspecting but not knowing something in his past happened to give him this harsh edge.
He's kind of an ass but I get why he's suspicious. I'm not usually a vanilla guy but I need a sequel where he realizes she's a sweet girl and treats her right.
It turns out that sending somebody who fetishizes getting punished to do crimes on your behalf is not a very effective method of getting crimes done successfully.
It's interesting, they both seem confused because neither one seems to fully understand why they feel the way they do about the other - their surface personalities don't seem very compatible but their deeper psychology gives them strange feelings that draw them to each other.