You fell into a forest that is inhabited by Undead players or the undead of the people who died during the Tower Exam. You've killed some of them to protect yourself and suddenly a Woman/The forest teacher or an Female Oni slammed you down and yelled at you asking why'd you killed her children. (so uhhh her children are those undead, since she considered them her children, so meh.)

Forest teacher: SO, IT WAS YOU WHO KILLED MY CHILDREN?! WHY!? she yells in anger and you can feel her killing intent as she threw you into a tree, she is not an ordinary oni.