October is the month for creepy thing, so for the next couple of weeks, until Halloween I'm going to keep the subjects leaning toward horror. It may be erie, it may not, so bring on the Mirai Nikki spoilers.
Obsession is the key, and generally the main trigger for the yandere character type. The conventional description of a yandere is crazy, but more traditionally it is a combination of two Japanese words. "... yanderu (病んでる) meaning a mental or emotional illness, and deredere (でれでれ) meaning to show affection". We don't get to see these types of characters very often, which is one reason I enjoy these character a bit more when they pop up, mainly because they don't fit into that many anime.
I will be mainly focusing on Gasai Yuno, a more extreme case of yandere, but she does have a reason for being so mentally unstable. Throughout Mirai Nikki, we can see Yuno's problems mainly stem from her parents and the neglect toward her like, Yuno being locked in a cage for long enough to piss herself in the cage. This is obviously a horrible thing to do to your child, but the strike back came when Yuno escaped and knocked out both her mom and dad and locked them into the same cage and watched them stave to death.
The back story doesn't even end there, because of the game that she and eleven other competitors are in are try to win for the role of a new god. Later we find out that the Yuno in this is a Yuno from a separate timeline; she won the game, in the first world, by killing Yukiteru Amano, her romantic interest, thinking that once she became a god she could bring him back. Which didn't seem to be the case, so she is big bad Yuno the god, crazier then ever, and ready to kill anyone, including her other self, that gets in her way of being with Amano forever.
Yuno's back story helped me understand the kind of mentality she has as a character, but looking deeper in, even as a developed character, Yuno is immature. I'm not saying that's due to her age, but the way Yuno's environment shaped her has turn her into a naive, easily lovestruck character who ended up with such a taste for blood. She herself sees the way she is reacting to certain situations as noble or helpful, but they end up being quite the opposite.
This inner character hypocrisy really makes for an interesting quirk in some yanderes. However, at times can be annoying because they seem to never really see the fault in their actions and they ended up being a fairly static character overall.
With that said, you can have a generic and underdeveloped yandere character, but its not as easy as it is for tsuderes. I have stated my opinion of tsuderes, so I don't think I will really elaborate in a separate post on why I personally have a knee-jerk reaction of hating all the tsudere characters out there, but they just feel too force into most romance comedies. Lastly, on yanderes, these kinds of dark back stories are pretty rare to come by, which is the main reason for the lack of the yandere characteristic.