Remember Ayano origins video? Alex never wanted to make her a
Yandere, he wanted to make "a game where a girl goes around killing people" (Lunar Scythe) and he needed a context for that, so he saw School Days and decided the context would be "Ayano is a yandere and kills for love".
That is all. He later threw some magic bloodline shit to justify her actions but made it worse.
I've read his godawful soulcalibur fic and it's obvious Alex has no fucking clue how to write women beyond his fave waifu stereotypes. Do you guys want to know why Ayano is like this? Lets look how her family works for a second:
http://yandere-simulator.wikia.com/wiki/Aishi_Family
-Literally born without emotions or reason to live.
-Somehow will fall in love with some random guy because her biological blood says so.
-Will only start developing emotions after dating her "unique" senpai.
-Her personality will be "molded" by how her Senpai treats her.
She is not written as a Yandere, she is written as a generic
slave in a very bad slave/master fetish fic. And if it sounds like i'm stretching, be aware that half of the fanfics Alex wrote ARE slave/master fetish fics.
https://www.fanfiction.net/u/868622/EvaXephon