Sayaka was a nutso murderer, while Kaede was a good person. There was a monokuma theater in the first one that talked about the difference between an intentional, premeditated murder, and one that occurs in the heat of the moment.

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Sayaka was capable of planning her kill, setting the stage, and framing her childhood friend, not only killing her target, but the rest of her classmates as well - and she did this almost immediately after the game started just for her own selfish wishes. I think she's as bad as Celeste, if not worse. As opposed to Kaede, who was trying to help her class, and refused to abandon them when she had the chance to get out for free.