The dead walking

This world use to be peaceful.. How did it become like this? Nobody knows why it started. The main character is Kira Higarashi. She has a close friend named Aliyah Kumara. She later then encounters new people named Kuroshi, Jose, Yurei and Thunder. They all have to trust and stick together, in order to survive the nights. Once the world shortens the population of humanity, more people go insane.. people who die, become the dead walking. Kira later changes more and more.. as she is not the same girl she use to be.. later as the days past.. more traumatizing parts start to happen and that's when she loses her sanity..