"All this happiness that you wished for me has been very hard to bear."
Miyatsuko's Heel Realization when Kaguya remembers who she is, and why she was born in the bamboo grove: she wanted to come to Earth to learn why another moon woman missed the planet, and broke the rules doing so. She says she doesn't want to leave her parents or her life, because despite how hard things have been, she was meant to be on Earth and cries out, "I don't want to leave!" Miyatsuko through Manly Tears says he loves "Princess" like his own child, and will protect her because she's still here. Kaguya apologizes for wishing she wasn't here, and goes My God, What Have I Done? because she wants to take it back.
As her father rallies his men to protect his daughter, Kaguya and her mother start singing the song about the bugs, bees and trees to stave off their nerves. Kaguya dives into a Dark Reprise of her version that she sang as a toddler.
The Hope Spot that Kaguya's mother smuggles her back to the village, where she reunites with a grown-up and married Sutemaru. She tells him "I just know I would have been happy" and starts crying. Sutemaru offers to run away with her and protect her. They even fly for a bit...and then she falls into the water, and he wakes up. "Little Bamboo" is gone. He thinks it was just a dream, but we see her walking back to the capital, resigned to her fate. And he walks back to his wife and child, resigned to his life as a humble civilian.
The ending: a procession of celestial beings descends from the Moon to abduct Kaguya, and Miyatsuko is unable to stop it, as every arrow his men fire at the celestial beings turns into flowers. An attendant offers Kaguya a robe that will erase her memories of her life on Earth, and she begs him to grant her a last moment with her parents before leaving for the Moon. What makes it even more tear-jerking is the happy tunethat plays during the scene.
Miyatsuko and his wife running towards their daughter. No matter their status, or what Miyatsuko did that hurt his daughter, they are her parents. Kaguya and they all start crying together, with her mother begging to go to the moon as well. All she can do is beg for their forgiveness.
The fourth suitor, instead of bringing her Buddha's Begging Bowl (or even faking it), decides to bring her a simple flower and plays to her interests. Even Kaguya is intrigued. However, it's immediately revealed that he made those same false promises to his previous wife. Kaguya bursts into tears, feeling awful for nearly falling for the ruse.
Just the simple fact that, if not for the fourth suitor's actual wife intervening, she really would've fallen for his false declarations of love. She came this close to giving her heart to Mr. Wrong.
Kaguya destroying her garden, crying out how it's fake, just like she is.
After the Emperor embraces her without consent, Kaguya does manage to break away, however afterwards she cannot shake off the feeling of being violated and hugs herself in grief.
Doubly so if one takes Word of God into consideration: Kaguya unwillingly leaving Earth? She's dying. She has known that she's been dying since when the Emperor came by and has been trying to come to terms with it, but can't. Despite how unhappy she is with her current life, she'd still rather live unhappy but together with the people she loves than die and leave them behind. Kaguya going to the Moon? She's passing on to the afterworld, a place with no sorrow, suffering, heavy thoughts or hurtful feelings; a place that she cannot return from, and that no one can follow her to. Kaguya forgetting everything about her past life? It's The Nothing After Death.
Perhaps even worse (or better, depending on your interpretation) is that despite supposedly remembering nothing of her life on earth, she still looks back in the end. Suggesting that a part of her does, in fact, miss Earth, but she'll never know why or be able to go back. It's hinted that much like the other moon resident, Kaguya will at least retain the residues of song and emotion on the moon.
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