Seikimatsu Occult Gakuin

In 2012, the Earth is overrun by aliens, prompting time travelers like Fumiaki to return to 1999 to destroy the "Nostradamus Key" and avert the apocalypse. In 1999, Maya, daughter of Waldstein Academy's former principal, returns to the school to take her father's place. Disapproving of her father's focus on the occult, she intends to sabotage the academy. Her plans change when she meets Fumiaki and discovers the impending doom. Together, they decide to search for the key.