Castaways are non-player characters that can be found in the Arc by finding a message in a bottle and using the treasure map contained in the bottle to locate the castaway. Progress of which castaways the player has found can be seen in the Arc Journal.

Once a message in a bottle is found and when a player has walked near its spawn location when it was visible[1] it will always be visible, unless the message in the bottle or its treasure map is in the player's bank or inventory. The castaways are marked as found in the Arc Journal after actually interacting with them on their islands.

Different bottles are available on different days, with the available bottles changing at daily reset (00:00 UTC) and the bottles appear on the same day for everyone.[2] Each bottle has a unique cycle[3], becoming visible once every few days. The cycle is a cycle of one day for the first bottle, two days for the second bottle, three days for third bottle, etc.

Selecting travel on Quartermaster Gully with any treasure map in your inventory will prompt him to ask if you'd like to travel to the island where the respective castaway can be found.

Some messages in a bottle are not possible to obtain without additional requirements:

Read the above for detailed information as to why bottles can appear on other days.

Each castaway will award the player a taijitu after being talked to for the first time. Finding all the castaways completes Castaways of the Arc and unlocks the [Name] the Castaway title.