Gokukoku no Brynhildr

Ryota Murakami, a high schooler haunted by the childhood friend he lost in a tragic accident, can’t forget the promise he made to her. Determined to keep it, he joins the astronomy club and searches for aliens—just as they once dreamed. One day, a beautiful girl transfers into his class. Her name is Neko Kuroha—and she looks exactly like his late childhood friend. Mysterious and strangely otherworldly, she carries secrets that defy explanation…

(Source: MANGA MILLION)