Brynhildr in the Darkness (2014)

S1E1 While I Wait For You

Murakami Ryota's childhood friend, Kuroneko, tragically died in an accident while attempting to demonstrate the existence of aliens. Years later, a new girl who bears an uncanny resemblance to her enrolls at his high school. When Ryota approaches her, Kuroha Neko firmly claims she isn't Kuroneko. However, as their conversation unfolds, she discloses an unexpected revelation that leaves him stunned.