Popularized in by the anime/visual novel School Days, yandere is a term for a psychotic girl who's only character traits are being cute or moe and random psychosis. The plot of a yandere story is that the main character falls in love with a girl who isn't the "yandere", where the yandere decides it would be a good idea to kill the love interest, any possible love interest, and finally the main character, because of love. Typically there is no reason for this psychosis because writers are usually lazy.
Rena from Higurashi is not a yandere.
Rena is not a yandere.
RENA IS NOT A YANDERE