I like your idea about the Buddhist nuns and the symbolic castration. I do agree that in an indirect way, Kuno-san shaving her head was her way of showing everyone that she would not be taken down by this, and that she would overcome without stooping to their level.
My initial reaction was that maybe by shaving her head, she was trying to make herself ugly.
The reason the girls hated her was because they were jealous and angry of her talent and her popularity among the boys. She can't make herself un-talented and she can't change her face, but she can shave her head. No boy (at least no immature high school boy) will find a bald girl attractive, and no girl (no shallow girl) would be jealous of a bald girl.
But this would be uncharacteristic of Kuno, who was a strong character. We know of her strength from Tsuda's comment, and from the way the actress portrayed her.
I'm still not 100% sure of the meaning or intention behind Kuno shaving her head, but I do like to think that it was an act of defiance against her classmates.
As for Tsuda, I think in a bittersweet way she was trying to combine her suicide with her dream of flying. In her mind she had to die, there was not much question about that I think that she decided that if she was going to die, she wanted to die feeling free (the way she never could) and flying like those kites in the air.

Careful there, the Eastern Asian and black people and Indians are Framling, the Na'vi are Ramen, and the wolves are Varelse acting as Ramen
. Which will mean perfectly nothing to you unless you liked Ender's Game. I loved it, and loved even more the idea of a Hierarchy of Foreignness.
there's a highway that is curling up like smoke above her shoulder

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Hey there Mr. Ambiguity, I just saw this. It's been quite a long time since I last watched (or thought about) this movie, but I don't remember anything about Kuno and renouncing men completely, or anyway be less interested in them than she was before the rape. But she may have done it to make herself look unattractive, as in "I don't want to compete with you girls and I don't want your attention boys just give me a fvcking break everyone".
Nice comparison between Lili and Lain. However, this theme felt a bit emo to me in Lili. One the other hand, the mystical chat phrases ended up reminding me of my own habit to radicalize various experiences (particularly the artistic ones) as a teen. We take sh!t awfully seriously at that age.
One more thing - I don't find Eastern Asian people particularly more similar to each other than, in general people from a different social group than me. I also have sometimes difficulties telling old people from each other (all those identical Southern German elegant old ladies traveling by bus on Sundays, white-haired and dressed in rose!), or children, or Caucasian men in movies from the late 70's when they all wore fat black wigs and enormous sunglasses. Or very blonde Nordic people. Or, even closer to my social group, a type of men from the Central Balkans, the thick, short and awfully hairy ones. Funny how the strangers are more similar to each other than the familiar people.
there's a highway that is curling up like smoke above her shoulder

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That's a pretty good explanation. I thought that Kuno's shaving meant that she wanted to make a radical change upon herself, to throw away the self that got raped, and become a new, resolute self that didn't get crushed by the terrible act performed against her, but I like the last phrase of your explanation better.
As to Tsuda, I think that her death was the result of something between deliberate suicide and an unavoidable accident caused by an act that didn't care about the physical rules of the world, in some metaphorical search of escape. Such as a fly attempt
there's a highway that is curling up like smoke above his shoulder

I think it was about shame and/or control.
Shaving your head is what buddhist nuns do. Maybe she wanted to renounce boys and sex. Maybe it had to do with shame.
At the end of WWII, people shaved the heads of women who collaborated with the occupiers. The shaving of a woman's head is like a symbolic castration.
By acknowledging the shame, she was expressing determination to go on living. She might have been saying, "beep you, everyone knows what you did. I appear in public and take control back despite what you did to me."

She killed herself in order to fight back.
The girl who was raped cut all her hair to show that she was not afraid of hoshino,tsuda saw it and thought herself was cowardice(that's way she cried).then she wanted to fight back,so she jumped off the electricity pylon.well, it may sounds strange,but shunji expained like that on his official web.

yeah, i think she jumped because when she was watching the people flying their kites she said that she wanted to be able to fly. so, i think she tried to from the top of the pylon, and thats how her keys ended up on the electricity wire.

I see. Cheers for the reply.

She had committed suicide. I think she was supposed to have climbed up the pylon and jumped.