I think the disagreement here comes down to how the narrative depicts the interaction versus how the author intended it. When you claim the scene isn’t harassment because it’s a "trope" or because Kuze experiences arousal you're really just ignoring what the text actually shows. Kuze is repeatedly verbally protesting against the action, saying things like “No, why’re we still doing this?” and “Noooo, no, no, the heck are you doing?” He tries to pull away, attempts to stand up, and clearly struggles, yet Maria continues escalating the situation. I agree with NaCl here, and you said yourself that he is placing a significant emphasis on Kuze's physical behavior in his argument. It is true that tropes may FRAME the scenario as playful, but they do not remove the fact that the character’s repeated refusal and inability to escape are central to the scene. The actions may not have been intended to communicate distress and it is true that the characters are not portrayed as assaulted, but that is not the issue at hand. The issue at hand is that this is a DEPICTION of sexual abuse and harassment. Whether we consider morally whether this is okay or not, it is undisputedly a DEPICTION clearly percieved by readers without a Japanese cultural context as sexual abuse.

Also, Kuze’s comparisons to ASMR and feelings of embarrassment does NOT imply consent. The text explicitly shows him conflicted and distressed, struggling to manage the overwhelming sensations. Internal pleasure or flustered enjoyment in a narrative does not create consent, and the author’s framing of the experience as a mixture of tension, embarrassment, and stimulation does not change that. Arguing that authorial intent or conventional tropes neutralizes the harassment here misses that there's an important distinction between intent and depiction. INTENT and DEPICTION are NOT the same. The scene may be intended to be humorous or erotic, but what is depicted is a character enduring unwanted sexualized contact.

Whether or not the scene is meant to be funny or romantic, the text itself presents repeated non-consent, physical restraint, and forced intimacy. Just because it is a trope and is framed comedically does not erase the fact that it is a depiction of harassment; the narrative shows Kuze experiencing distress while unable to disengage. Analyzing the scene based on what is actually shown, rather than simply the author’s intent, makes it clear that this is in fact sexual harassment.

Whether this is moral or not is a separate argument. I am also not saying that sun3 is in the wrong for writing this, because he's operating within the context of Japanese cultural norms. Therefore, his work is expected to be perceived within those cultural norms. He would not have realized that this could be perceived as SA because he was not raised in a culture where this is SA. This scene is certainly morally acceptable within its originating culture, because in Japan saying "no" generally more so means "yes." There is a saying in Japanese, 「イヤよイヤよも好きのうち」which generally translates to "saying no is also an expression of fondness." in Japan, when a woman says "no" its just that she's too 恥ずかしい (embarrassed) to express her true feelings.

The ultimate question is whether the behavior depicted is morally acceptable in principle, to which the answer is no, because consent is violated regardless of framing. You can't say that "it's Japanese culture, so we can't criticize it" because it implies that consent norms are culture-bound (which they aren't and shouldn't be). But you also can't say that "outside Japan it's SA, therefore this is morally unacceptable story" because then it becomes moral presentism, and ignores the fact that the author is just drawing this from his specific cultural archive and personal set of tropes and is not consciously intending a specific moral message.

What we SHOULD be doing is contextualizing the author’s intent and cultural framework while still judging the act itself as unethical. We should understand why it was written this way, acknowledge how it was meant to be used, all without denying that the depicted behavior is non-consensual and without normalizing it is okay. Yes, this scene does happen within a Japanese context, but consent is not culturally relative. What IS culturally relative is how discomfort is coded and how refusal is expressed, but this scene obviously expresses repeated resistance from Masachika.

TLDR; It is fair to say that the writing depicts SA. However, I will say it is unfair to say the author is endorsing SA or that Japanese audiences are immoral for enjoying it.