My 3rd review about anime which made from its game, please enjoy.
A group of students from St. Luminous College are investigating the mysterious disappearances that are happening all around Tatsumi Town. One student, who was researching a book entitled ‘End Earth’, which describes an alternate world, also mysteriously disappears. As Mao, a being from the other world, enters their world in order to look for her friend, Zero, she teams up with Souma and Kureha in order to battle a monster who also came to their world. Just when things seem to go their way, an accident teleports Souma and Kureha into another world. To make things more complicated, Zero appears to the two stating that he will now entrust the world to Souma. As they travel this new world, they encounter familiar friends and enemies, and they begin to realize that getting back to their own world is harder than they previously thought.
In End Earth, a war, surrounding a legendary item called “The Holy Grail”, begins. Zero later tells Souma that the world will end if Zeroboros, the guardian of time and space, awakens. This guardian will use whoever wins the war as a body.