In an instant, Rikka's life was forever altered. During a school excursion, the bus she was on flipped and plunged into a lake, leaving everyone on board to drown. For some unknown reason, Rikka was the sole survivor, but her salvation was not due to sheer luck. Subsequently, strange occurrences began to unfold as she was repeatedly attacked by a water-loving female with the same name as her. What does this sadistic Rikka desire from our protagonist, and what was the secret to her survival in the lake? Who gifted her with this power, and for what purpose?