The name of Day of Departure refers to a worldwide time period where the Legendaries that had taken upon the protection of various realms such as Johto, Alola, Suocé or Estracura, disappeared from public record.

The event was prompted by the events of the burning of the two Ecruteak Towers. Irate at the destruction of their perch and the invasion of their home grounds, the Protectors Lugia and Ho-Oh took off from Johto and abandoned the region.

Over the following days they each went their way across various continents, saddened and depressed, singing a song about the betrayal and invasion they had suffered by the hand of the humans. Wherever they went, other Legendaries heard the song and interviewed with the two Protectors, then ended up relieving themselves from attachment to the human realms as well.

This event shaped many relationships between Legendaries and other realms in present times. It is the reason why the Cadrícea Muskedeer Trio remained aloof previous to the events of the Pokefutures reveal ( Forever Catch ), it is why Zygarde did not watch over the Flower Weapon in present time, and explains lack of awareness in modern Hoenn that the golem trio from the Snowpoint Temple was hosted in the region.