For some reason, there's this myth that it's the number one rule in a "___ x Reader" story to not actually kill the reader?
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What?
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*coughs* BULLSHIT!
Whomever told you that is a lying piece of garbage.
Are you expecting the reader to kill themselves, are you wanting a happy ending to this sick little love story?
Yanderes will either kill the object of their obsession or be killed by them instead. That's just how it goes, okay?
So no, no it's not the number one rule of yandere to not kill the reader.
Kill the reader if it fits the story. Kill the yandere if it fits the story.
Obsession never ends with a, "And they all lived happily ever after. The end!"
YOU LITERALLY JUST SPENT THE ENTIRE STORY EITHER MURDERING OFF PEOPLE OR ISOLATING THE MAIN CHARACTER!!! Who the fuck is happy after that? Certainly not the fictional people that you just killed. The yandere sure as fuck ain't too happy that they're no longer in the picture.
There are no happy endings in a true yandere story.
If you think there are, you're the twisted one and not the sociopath that you want to create.
Yandere literally means "Mentally Sick Love."
Use your head!!!