Brynhildr in the Darkness

While I Wait For You (1x1)

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Murakami Ryouta's best friend, Kuroneko, died in an accident trying to prove aliens existed when they were kids. Now, a girl who looks just like her transfers into his high school. When confronted Kuroha Neko insists she isn't Kuroneko, but she ends up revealing something else even more surprising...