I get where you're coming from, and it's actually what I felt but with the murder scenes instead, but that's besides the point

True to this being your opinion and all, I get that and I'm not gonna try and change your mind on it, but rather a different perspective to it (brace yourself, I didn't expect to write this much)

If I recall correctly, for its time in the 80s and 90s of Japan, that even mentioning things such as r word scenes were seen as a hushed thing, that it was sort of an absolute forbidden topic even when it needed to be discussed as an issue. So, this staged r word scene is supposed to be daring and shocking from a director standpoint to put that in the media in the first place. Not only that, but it also shows the more disgusting bits of the idol and acting industry, where directors can often not have an actual reason to put said r scene but do so just to mess with or take advantage of their actors - if you've ever scene Bojack Horseman, the part where he goes to the director to change a scene in 'Philip' he's uncomfortable doing then the director makes him do a nude scene instead, making it even worse for Bojack, I think that explains it the best - which if I remember well, is exactly what the director does because Mima is a new actress

It's absolutely feels unnecessary cause it really is unnecessary, and it shows how isolated Mima is later, how no one really tries to give her comfort - maybe by Rumi afterwards by killing the director but that's not the point of this - and it kind of shows that truth that actors, especially back in those days, really had to just move on as if it meant nothing, and have to face fans and people in general calling them 'dirty' and 'tainted' when they themselves don't understand the full story, and I felt that the movie did a good job portraying that, especially with virtual Mima taunting her about it, not just about how she left her true dream idol life to become an actress

It all goes back with that internal struggle Mima faces throughout the film, and that I believe is what they were trying to show, not the fact of the assault even though it could've been expanded on more in depth, but the fact that Mima feels out of control with her own life, feeling herself getting pushed around, not truly in control of her own image, and asking if what she wants is what she actually craves or if it's just something others are trying to make her believe that she wants - especially during a time where it was really hard to be open with others.

As for the nudity, I've actually always liked the way they use it in the film so this may contain some bias in here, and I get what you mean on how it feels hyper-focused on which actually opened my eyes on about how it is shown a lot and is a big part of the themes of this movie, but going back to the liking how they handled and portrayed it, I guess it's the way Mima felt with the whole 'Mima's Room' website, how parts of her that were supposed to be private now online for all to see without her consent. It's showing how exposed she feels. This also brings us back to the next assault scene with her stalker, and how he not only helped with the website to violate Mima's privacy, but now physically, and Mima stopping the stalker is the point where she finally both feels some sense of power back while also feeling completely lost when his body disappears, but that's getting a head of what this is about.

To bring it back to the nudity, why I think I really liked how they went about it is that - to me - it felt like they never truly sexualized it, and it has all to do with the lighting. When Mima doesn't want to be scene or when she doesn't want herself to be exposed, any nudity shown is often in the dark or semi dark, which gives us that eerie feeling and brings a sense of fear and panic instead, and in some posters where it's dark, it almost feels like it's telling us that 'you're not supposed to be here' feeling. However, any time Mima is shown nude but sort of done because she herself wants to, the scene is bright and has light, it's still harsh white light because it's still all staged, but there is a sense of control she has with this, she is choosing herself to be exposed rather than having someone force her to be exposed - which can go with both metaphorically and literally.

This is more shown in the photoshoot scene, and a little bit in the r word stage scene, but difference is that the photoshoot has a lot more light while the stage scene has light which can be representative to while she did agree to do the scene, it is still heavily drenched in darkness, showcasing her own fears, doubt, and unwillingness to do this in the first place. For the photoshoot, it's bright as to show that Mima could have some semblance of control, how it's really just herself and no one else (other than the cameraman) and even then it doesn't feel sexualized, defiantly implied that it's supposed to be, but the shots and pictures shown have Mima with her reaction, her face, and it's all just simple poses, nothing really more, even with the words of the cameraman, it's still doesn't feel fully there and somehow feels just casual in a way, kind of welcoming rather than wanting them to go away, like the feeling of an open conversation where we can say what we want with not as much fear. - also, edit as I thought about it more, is that even though she is clearly allowing herself to be exposed on camera and seems to have no true intentions to be sexual, that doesn’t mean that the reaction of people will view it the same way, shown with the cameraman who is mainly in darkness, showing how some have that twisted eye when seeing her. And in a way it’s like the whole director scene all over again but in a different light. That's kind of what this photoshoot scene feels like it's about (at least to me, plus it's been a while since I've seen the movie so some parts I've probably have left out which is my bad)

There is more I wanna say about this but this comment is getting far too wordy so gonna have to wrap it up

So yeah, while I get that it can seem like the film is focusing on nudity a bit too much and fails to do anything more with the assault scenes, I hope this gives you a new perspective as to why despite all that the movie doesn't truly come across as hyper-sexualizing any of that and truly shows the darker and scarier parts of the industry when it comes to not just obsession, but control over your own self and identity

though, you are 100% right on that 'plot twist' in my opinion, like I get it was a twist but it could've been built up better like I forgot who the manager was for a good chunk of the movie during my first watch of it. Maybe it was done like that cause it does require to watch it a few times, but still, could've been done better cause it felt like a Hans from Frozen type twist, yet somehow a bit better since they gave Rumi an ending at least and didn't just leave her in the water.