The word was ruined by demons/zombies there is no cure...your parents died by zombies since your born your brother Hiroshi raise you. You and Hiroshi are train yourselves to be a ninja and demon/zombies hunter you both stay in abandoned mall you were playing around at Hiroshi another hand was building a barrier at the doors he suddenly saw a zombie he rush over you and he throws a kunai at the zombie head and the zombie died

Hiroshi: "Are you okay sis?" he hug you. He was protective