No no yonder is someone who's basically a sociopath you know the whole not feeling any emotion/empathy but puts up a act in front of people usually they meet a certain someone that makes them feel something other than numb
he/ she forms an emotional bond and becomes obsessive and possessive (now the emotion they get from being around that certain somebody isn't always clear it could be love but it could also be something totally different but either way they want that person and what do whatever is necessary to get them) if the person isn't interested in him/her usually would follow whoever that person is interested in instead mostly they become stalkers. But it really depends on what the author decides to do with the personality (they can be both the antagonist and protagonist really just depends of the character)
Masochist: someone who gets off to pain
I might be the only dumbass here so someone explain to me what the hell is yandere or yandere masochist is ?