It reaches a point where, after she confesses her love to the protagonist, she stabs herself to death out of over-excitement or rejection (depending on the protagonist’s response to her confession, both lead to the same outcome, courtesy of Monika). She is ultimately unable to control her obsessive outbursts. And she simply wanted to use Yuri’s unorthodox interests and awkwardness to make her seem unappealing. Sayori and Yuri die as a side effect of Monika tampering with them – she originally wanted Sayori’s depression to simply prevent her from confessing to the MC in the first place, out of fear of rejection. It makes perfect sense therefore why she dies no matter what you do. In Yuri’s case she either kills herself out of despair if you reject her or, because she cuts when she gets excited, stabs herself if you accept her confession. You might be interested: Question: Quest In Literature? Will sayori always kill herself?
