Kuro Hitsuji no Ayumi

The protagonist, Asahi, has returned to his hometown for the first time in seven years. On his first day at his new school, his joy at reuniting with his beloved childhood friend, Haruhiko, is short-lived when Asahi catches sight of something terrifying outside the window. In that instant, the classroom is enveloped in an eerie atmosphere—?

(Source: GANMA, translated)