There are many states of being in this world, and some have managed to become immortal and gain the ability to manipulate nature at will to a certain extent. People called them deities and they are very difficult to tell apart until they exercise their divine power in public. They will sometime drop by the land of the living for an excursion to experience suffering and even dying. With exception to being banished there due to punishment, I am wondering why every deity must abandon their immortality when entering the realm of the living. The gatekeepers, which are ethereal mythical creatures, will prey on anyone who dares violate the code and will proceed to devour the suspect with extreme prejudices.
Procedure for a deity visiting the realm of the living:
Step 1: notify the higher up to get the visa
Step 2: visitor must seal their immortality into the passport (call 1800-DEITY immediately to replace lost/stolen passport)
Step 3: now proceed to realm of the living (visitor must produce a valid passport during check by gatekeepers)