Since the Divine Medicine War was about to begin in the Devil Realm, Great Mystic Art Users from all four realms would gather there.
Of course, not every Great Mystic Art User would come. At least one-third of those in the four realms would be present.
Within the four realms, once the Divine Medicine War began, Great Mystic Art Users would by default be permitted to travel between the four realms, no longer subject to any restrictions.
Under ordinary circumstances, if a Great Mystic Art User crossed into another realm without permission and was discovered by an expert in that realm, it would be an enormous crime.
Even if that Great Mystic Art User died within the realm, his friends and family would have neither the qualifications nor the justification to come seeking revenge or justice.
Thus, in ordinary times, Great Mystic Art Users traveled between the myriad realms with the utmost caution, lest they violate any taboo.
Even during the Divine Medicine War, many Great Mystic Art Users who crossed into another realm would usually notify the "sect or lineage in power" of that realm.
For example, this year's Divine Medicine War was being held in the Devil Realm Eastern Region.
Therefore, after warriors from the other three realms arrived in the Devil Realm Eastern Region, they would first visit the four Flourishing Sects there.
That was why Lin Bai had previously encountered a Great Mystic Art User from the Demon Realm in Nine Underworlds City.
Of course, the Great Mystic Art Users willing to "pay their respects" came bearing proper etiquette. They did not want to cause any other trouble.
There were also many Great Mystic Art Users who refused to give notice. After entering the Devil Realm, they wandered everywhere or headed straight for the Burial Earth.