Let me clarify a few things.
@Starstorm1
1&2) My point was that there's not much justification in him going around and beating up random people. The word excuse was used incorrectly and I apologize for that. What I meant by everything was that it was rather surprising to see him suddenly change into a completely different person. He has a strong conviction to rescue his sister and that is worthy of respect, but when he resorts to arbitrary violence that really can't be justified at all, especially when he hated it at one point... Well, I don't like it. You can support this sort of behaviour, sure, I don't care. If Maria's goal for him to fight on the street was to "need to know how it feels to fight with someone who doesn’t use rules" as you said, I think there could have been a better way to do this. Those thugs were probably not great people, in fact, they could have been the worst sort of people, but they could have also been people that were completely innocent. Innocent until proven guilty. Find garbage people and then beat them up. In my opinion, just indiscriminately going around and severely injuring strangers is a little over the top. Maybe he doesn't have enough time to go around and make sure the people he's beating up is trash, but honestly, this ruthlessness is just... It's quite painful to watch for someone like our MC who was so righteous and kind before.
2&3) I didn't mean that his sister's life isn't worth saving if she's changed into a horrible person. The fact remains that he blames himself for his sister's capture and will do anything to save her. All I'm trying to say is that it might not be worth it in the end. He will do it, he will continue on this path and he will continue to sink into the darkness. The end will most likely be all happily ever after, but perhaps he should consider other people other than his goal and his sister. Yes, saving his sister can only be done if he joins Fight Class 3. That doesn't mean he has to turn into a psychopath to do it. You do not need to lose all of your morality and humanity. Maybe this is a naive way of thinking, but the concept of integrity and fairness is naive. Honestly, I just wish he would think about other people for once. What about his friends? Yes, they are not his 'babysitters' but I think he's quite selfish in how he's behaving. Of course, his goals are important, but he pays zero thought to other people and is honestly blinded at this point... I'm pretty sure his friendships are going to be wrecked after this...
4) I disagree with you. The foreshadowing is either non-existent or lacking. There probably is some and I probably missed it but I don't think a 'little bit' is enough. You can disagree with me, that's fine. Furthermore, in 71-72, we do see a kind of breakdown, but we don't see the aftermath. By the aftermath, I mean, when we see his mindset change. In chapter 71 he wants to stop but Maria humiliates him so kind of a breakdown, I suppose. In 72 though which makes me really confused, he says he doesn't want to fight and then he goes like "I can only find my sister if I fight", so now we got strong resolve. So a bit of change in perspective here. Which is great. But then, he goes back to "why did it turn out this way? Why am I so weak" Okay, so we see here in 72 that he's still unsure about this whole business. But then starting at the end of chapter 74, he goes wack, especially in pages 5,6,7 for chapter 75. Like he was unsure, tired and depressed in 72 but now he's absolutely gaga and totally fine with violence in 75? Unless he's pretending or something, it's a little bit weird... Obviously, in the next chapters, he's changed completely, but I think the author could have done more in the transformation process. Frankly, I think there are places that could have been improved or are completely missing. Yes, I should have acknowledged the buildup in my other post, but I think there could have been more done. At least, I think we can agree that it was a little bit abrupt. Or if you don't, that's fine.
Again, if you have a different opinion, that's fine. I'm not trying to convince you or anything. In fact, thank you for presenting such a well-thought counter-argument, I really appreciate it. It's been a while since I've had a friendly debate 😃