MC killed the brother solely because he was being forced to be his accomplish in raping a girl. He didn’t want to and fought back, and actually killed the brother when his emotions were running wild (because of his trauma with his own father being a rapist too). So yeah, while killing is wrong, I cannot blame him, the brother deserved to die. The girl, while loving her brother very much, managed not to be biased in the end. So Kudo to her.
I like how the author portrayed her feelings in a very realistic way too. While she loves the guy, her adoration for her brother all these years didn’t lose to that love, so she actually wanted evidence to catch the guy. Even when the guy told her his story she couldn’t trust him 100% and only trusted him when she has enough evidence. Despite being a very emotional girl, she didn’t let her emotions control her judgement and that’s very cool.