@shacchan
Checked again, only the girl was in the same school yes. And she did help him half-heartly, which is why it didn't work (she stopped once the bullying and that's about it). The brother said it himself, to not start helping if she can't keep going untill the end. Then she stopped.
What I don't like in general is that everyone seems to be seeing him as a lost cause. Someone who was seen as trash by his parents, bullied at school, having both parents dying and, the hardest of all, having a sister who doesn't know about all this treatment. I feel like he's been keeping up pretty well until high school, but he eventually broke down. Now, instead of helping him recover, people keep looking down on him, treating him like trash. In the end, he and his sister are the "strongest" character of the manga imo, because even being seen as trash throughout his whole life (even by MC and friends), it looks like he'll be able to recover. I just hate the fact that someone who put so much effort to keep up a good life, eventually breaking down, and now starting to walk forward, is seen in such a bad way by MC&friends. He's been through enough sht, instead of calling him names and punching him they should maybe try to help for real for once.