Clock Zero: Shuuen no Ichibyou

Kurou Nadeshiko is twelve years old, the daughter of a wealthy family, attending a prestigious school alongside her childhood friend and quietly planning to become a doctor one day. Every night she has the same dream: she is in her twenties, standing in a ruined world she does not recognize. When a transfer student named Kaido Takato arrives in her class, she is drawn into an after-school activity called Clock Zero — and the two worlds of her waking life and her nightly visions begin to overlap.