This was beautiful and poignant and tragic and brought me to tears. I'm more coherent now so I can spill my guts on all the things I liked about it. Forgive me for my rambling.
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I love the use of visuals throughout the story, both the watercolor-like illustrations and sprites themselves, but also the use of colors for the text. It not only made the NVL-style format of the dialogue easy to read/understand who was speaking, but also to me highlighted the emotions of the characters. The way Rose's scarlet-red turned softer and more pink when she was being intimate with Cori and turning dark-red again whenever she was being critical of it, and Cori's dark green turning a lighter shade and back again depending on the situation she was in.
The prose was absolutely amazing. The way you wrote the characters' emotions, the physical sensations, it was all really well-done. You can feel how intertwined Cori and Rose were and how much they clung to each other despite the awful things she did. But there were good moments too, and the story didn't downplay or shy away from how much Cori loved Rose. The final scene hit me like a punch, and the letters did especially. I read all of them and cried.
There is so much more I could say but for fear of making this seven more paragraphs: This was such an amazing story to read. Thank you for sharing it.