Brynhildr in the Darkness

In his childhood, Ryouta Murakami used to hang out with a girl he called Kuroneko. She loved star-gazing and so they looked up to the stars together every night. Kuroneko ‒ whose actual name is a mystery to him ‒ insisted she knew about aliens. One day, she decided to show him these aliens she was talking about, but an accident occurred and Kuroneko died.

Years have gone by and Ryouta now is a member of the astronomy club, obsessed with finding the proof for the existence of aliens. One day, a transfer student called Neko Kuroha ‒ who is the spitting image of Kuroneko ‒ enters his class. She is at least as odd as Kuroneko and starts claiming that she knows whenever someone is going to die ‒ which is proven right, after her prediction for Ryouta almost became reality.

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When he was a child, Murakami was infatuated with a girl he called Kuroneko. She insisted on knowing about aliens and having met them, but no one believed her, even young Murakami was skeptical. One day, she decides to show him the aliens, but an accident occurs and Kuroneko dies while Murakami is left seriously wounded in the hospital.
Years go by and Murakami obsesses on finding proof of the existence of aliens because of a promise he had made with Kuroneko. Then, one day, a new transfer student comes to his class, who not only looks a lot like Kuroneko, but is named Kurohaneko!