The story tells a boy named Ryōta Murakami and his female friend he calls Kuroneko. The two have a close relationship as they look up at the stars in the sky. One day, Kuroneko insists that aliens really exist and attempts to show them to Ryōta. However, they slip off a dam and get injured. Ryōta survives the accident, but the doctors claim that Kuroneko has died. Feeling regretful since then, Ryōta continued looking at the sky in hope of becoming a researcher for NASA to prove the existence of aliens as atonement for Kuroneko. Ten years later, Ryōta is now a top student in high school. Suddenly, a transfer student named Neko Kuroha enters his classroom. Surprisingly, she looks exactly like Kuroneko, however, she does not recognize Ryōta. During swimming class, while Ryōta remains concerned about Neko, a student almost drowns but is saved by a mysterious force. Ryōta goes to the observatory as the sole member of the astronomy club. Neko comes in to inform Ryōta that his death has been predicted, but he treats it as a bluff. As the two come to know each other, Ryōta becomes suspicious of her as she doesn't know her multiplication tables and possesses inhuman strength. Ignoring Neko's warning, Ryōta leaves for home without getting on the bus when a mudslide suddenly comes down on him. A boulder is about to crush him, Neko splits it with strange powers; saving Ryōta. Showing a harness attached to the nape of her neck, Neko reveals to him that she is a witch.