The Rift between the present world and the alternative world caused by the instability of energy is the only passage to the present world for the monsters in the alternative world. In order to block the invasion of monsters, in the present world, a group of people with special power bravely went into the Rift to defend the world.—Bilibili TV

Unstable energies of the present world and an alternate realm has ripped open a rift of time and space. It is the only passage where monsters from the alternate realm can enter the world. To stop the invading monsters, a group of chosen people step forward to fight and protect the world at the rift.—MyAnimeList

Unstable energies of our world and another realm have ripped open a rift of time and space. It is the only passage where monsters from the other realm can enter this world. To stop the invading monsters, a group of chosen people steps forward to fight and protect the world at the rift.—Bilibili, YouTube, edited