I think the best place to start is theming. So the true theme in Uta Kata is growing up, but specifically growing up under deception.
Every consistent part of the series rings true on this. Ichika is lied to and exploited.
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At first its fine, and as the series progresses, it becomes frustrating.
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About half-way through, Ichika starts realizes her eyes are glowing red, and her transformations become more violent and less under her control.
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And this is where I take a step back, because, in my opinion, this is supposed to stand in for society.
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Uta Kata does this only at the end, and for a particular reason. The rules dont actually matter. At all.
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Ichika doesn't know or care about the rules, the test, or even the powers once the start to hurt her. She takes this all under false pretenses.
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Ichika is living with arbitrary rules, for a power that she doesn't really want, that starts hurting her, and rules cut her off at every turn.
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The rules dont matter because its more about the pain inflicted.
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Well, because of Ichika. Ichika, the main character is quickly shown as a sweet, kind-hearted, obedient child who likes having fun with her friends and just enjoys life.
The obedient part in particular is important.
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In the middle of that she starts losing control of her powers, and they begin to come and do what they want.
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She's constantly betrayed and at odds with herself.
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You don't find out why til the end, but the ultimate point to me is that Saya, who herself is a full lie, forces others to lie and be silent around her for the purity of this test.
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If its not obvious, Uta Kata is a bit of a mess.
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Its about a girl led into darkness to fumble and stumble into negative emotions. Its messy, because it tries to convey just how messy coming to terms with growing up is.
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Both series leave you in the dark in many regards because many of its answers a left open ended, and frankly needed to confuse you for a few reasons.
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...but how does it end?
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1) Saya is a Djinn, and possesses Ichika
2) Sei her home teacher has also gone through this, and he tried to tell her stuff and therefor broke the rules and was turned to Stone
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4) she reveals the nature of the test. Im slightly foggy on this a bit, but it boils down to, the gods have a human channel Djinn, and their inner emotions judge humanity's worthiness.
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A) sacrifice herself for humanity, or sacrifice humanity.
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Anyway, this is where my favorite bit kinda happens. Ichika rejects the test and refuses to answer, saying that she doesn't want to sacrifice either, standing firm even as Saya tries to hurt her, and IIRC Ichika regains control
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And the series ends, as Ichika and her family moves as she gives her friends goodbyes, and Saya's boss tells her that maybe this result may be true.
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