The Border (the Forgotten Ruin Dimension)

It is used to be called the Forgotten Ruin. It is a place linking the Demon Realm (also known as the Underworld) to the Heaven Realm. There's a limited amount of time that allows people to cross over the realm. When the time is up, the dimension will shut off and people will be stuck there until the dimension is opened up again.

During that time, no one can know what happened to the souls that were stuck in there. It is common knowledge that demons and angels have always been in conflict for ages, so there's no guarantee that they will come back safely...