You can reduce anything like that to make it sound shallow, though. That, and it's not a random teacher, it's the teacher that raped Kaede.
Tsubasa doesn't realize Kaede's emotional pain through getting stabbed-- she interprets the stab as punishment for hurting Kaede in her ignorance of his trauma.
Myself, I don't have a concrete criticism of this sequence, though I can't shake the idea of it feeling "flat" despite it being high energy. That's especially not a material criticism, though. I think the closest I can get to making that criticism material is by noting the following:
1. The rapist teacher comes off more as an anthropomorphized vector of violence and trauma that Kaede has to overcome in order to complete his arc, than a character in her own right. It makes sense for Kaede to have that perspective, but the reading perspective we're given isn't that intimately anchored in Kaede's perception. My impression is probably also caused by the fact that she's up to now been a character that's only existed in Kaede's recollections and trauma-- and now she shows up in the real, out of nowhere, full tilt as an entirely different person. All of these are altogether plausible circumstances, but I don't really dig what it all culminates into. And I don't even intrinsically mind contrivance, but it might be that I can dig naked contrivance when it's instrumental to a theme or motif, or is still grounded in how the characters act-- and this is neither of those.
I'd have appreciated a character exploration from her perspective-- no, not to make her sympathetic, but more so because I think it would have helped establish that Kaede got raped by a human being and not merely "a rapist".
2. It's thematically a good thing that Kaede gets to declare that he'll prove that he can be happy directly to the person that robbed him of so much, but narratively speaking, he does it in the middle of a hostile situation with a woman swinging a knife around that already stabbed someone else while trying to get to him. Between this and my previous point, it feels hokey to me.
She was at the back end of the previous chapter.
I'm not who you were replying to, but let me take a stab (😉) at explaining the criticisms of this. As an aside, technically, it was a slash, not a stab, but even I don't really care.
You're right. The sensei is a plot device and not really a character in this chapter. In the flashback arc, we got two chapters devoted to her personality. It gave this message saying even a person you trusted can do something horrible. Or something. But then this chapter happens, and it's like...none of that mattered. Who the sensei was doesn't matter here, and she is used to drive forward action and drama.
And yes, that sometimes does happen in real life. Personalities can change drastically. But that doesn't make for a good
story, a narrative where the author could've, if the author wanted, elaborated on how and why that happened. In real life, I can't see a flashback of your past, but in this work, the author just made the sensei a shallow tool.
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And, honestly speaking, that isn't the first time the author has done something like this. Sahara, the self-proclaimed possible asexual classmate, was not really that developed as a character. As another commenter stated, he gave a textbook definition of asexuality.
There was Aya's lecture to Tsubasa, specifically using miniskirts as an example. That also comes off as lacking depth. However, I can accept both of those specifically because they come from teenagers. They might have looked it up online. That's not that bad.
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But then Kaede gives his speech about finding happiness and moving past his trauma... I was honestly almost laughing at the absurdity of him being that dramatic in the face of someone who is swinging a knife around.
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All of that criticism can be summed up in short. The author tried to make this look deeper than it actually is. The author resorted to shallow methods and writing while trying to be dramatic.
It's the same kind of thing as "It was a dark and stormy night". The author thought they were being deep and edgy.
I'm bashing the work, obviously, but I still generally found it enjoyable, as a whole.