Umi Monogatari: Marin no Kore Naani?

A young girl discovers a mysterious object in the ocean, which leads to a series of events involving the supernatural and the unknown. She becomes involved in a strange phenomenon that defies explanation, drawing attention from others who seek to understand its origin. The object appears to have a connection to an ancient legend, hinting at a deeper mystery beneath the surface. As she investigates further, she encounters eerie occurrences and unexplained forces tied to the sea. The story explores her attempts to uncover the truth while dealing with the unsettling nature of the events unfolding around her.