/jp/ - Otaku Culture

Ok so I just finished my first VN in Japanese (Ciconia) and I need advice

Just before this scene, a character rants at the class for being lazy. This is the narrator's take on his rant. My issue is that I cannot naturally parse this narration, because I can't consistently deduce what the narrator is talking about.

I think the reason why I'm confused is because there is no は.
I checked the English translation (I never really do this but I felt defeated) and understood that the narrator was talking about the character that literally just ranted because of the pronouns used, but I wouldn't have assumed that in Japanese due to the lack of a topic marker here. How can I fix that? Is there a consistent way to deduce what the topic is even when it's not said? Hope my question makes sense.