Latios is a descendant of the famous Latios and Latias that saved the city of Alto Mare from a great evil. It spends most of its time in the Secret Garden so that it isn't seen by the residents of the city, though it often ventures out into the city by making itself invisible so it can watch over its little sister who is always curious to find out what is going on.
When
Oakley and
Annie arrived in the Secret Garden, Latios was able to protect Latias long enough for her to get away but Latios was captured and taken to the temple so it could be used to activate the Heart Drop machine. Latias recruited
Ash Ketchum and together they were able to rescue Latios.
As the tsunami wave approached Alto Mare, Latios combined its energy with Latias and they were able to stop the wave. Unfortunately, it sacrificed itself in order to protect the city.