A Yandere relates to love or admiration. The term is used to refer to someone so in love with someone else- it leads them to act out in violent ways. Normally this is done by targeting their obsession or those who get in the way. Rarely, a Yandere may be played for laughs as a momentary gag or ignored all together.
Yandere is a person who is initially loving and caring to someone they have a strong affection for until their romantic love, admiration, and devotion becomes feisty and mentally destructive in nature through either over protectiveness, violence, brutality or all three combined. It's like a hole in their life that they NEED filled by something. Oh and of course a yandere could also kill an S/O if they're extremely delusional and believe their love interest has somehow cheated on/betrayed them. Jealousy is a good trigger for murder by yandere. In short, the reasons mentioned there are: * The unfaltering devotion of the characters to the one they love. * The out-of-the-norm nature of those characters. So, they may seem more "interesting" to some people and/or make the show more intense. A Yandere has a split personality just like a Tsundere does. Around a lot of people, they act sweet, caring, cute, shy, happy, and any other normal way to act unless someone performs/does any actions that may be unwanted. ... Whoever they love, is the person they will go full Yandere for. Yanderes are typically possessive, extremely jealous, and willing to do anything for a love interest., yanderes will exist in real life, but it is very rare they will commit violent acts. Yanderes are outwardly cute and/or innocent girls who become violent and obsessive because of love. Yangires are outwardly cute and/or innocent girls who have a completely batshit crazy side and quickly become violent without warning. ... A classic example of a yandere is Yuno Gasai from Mirai Nikki. What can cause a person to become a yandere? Usually they basically have borderline personality disorder, which has a lot of potential causes. In anime it's usually just a trauma or their dad/parents or something, probably. being locked in a cage by their parents.
It's a form of possessive obsession. It's not killing that makes a Yandere, it's the constant threat that they are capable and willing to do extreme things over their feelings for someone with very little needed to trigger them. This includes killing, but does not necessarily imply that someone is murderous.
Being a Yandere or Tusn or any form of dere has less to do with physical interaction and more to do with personality. You don't need to physically abuse your love interest to be a tsun and you don't need to murder everyone that's close to them in order to be a yan. Whenever their love is threatened, yandere tend to be “supremely selfish” kind of evil. ... This kind of girl is a murderous psycho all the time, but she also knows love. You can argue this kind of person is quite evil.