everywhere you search a yandere is violent and possessive but not according to some ...
roflmao...
Yandere
Noun, Noun or verb acting prenominally
1. person with an unhealthy romantic obsession Slang, from 病む(yamu) and デレデレ
病む(yamu)
Godan verb with 'mu' ending, Intransitive verb
1. to fall ill
Godan verb with 'mu' ending, Transitive verb
2. to suffer from (e.g. a disease); to have something wrong with (e.g. an inner organ)
So, as you can see, doesn't mean they have to be violent to others or their love interest. They are just typically portrayed as violent and possessive, because that's the easiest to show and it's flashy, etc.