This series justifies Sae’s personality and perspective. She was full of insecurities and instead of improving herself, she’s doing bad and annoying things as her defense mechanism. She acquired it because of her sad childhood. And her parents did not help to her situation.
It was also shown here how she became Momo’s friend. I think Sae felt empty after she knew all about Momo. Hence, she copied her endlessly, out of admiration & to fill what’s missing in her. She thought by pretending to be Momo, she can be happy like Momo. But what she only lacks were trust & honesty.
(i love the extra chapter)