This orca stranded and was rescued by Hayako several years ago. She took it to the aquarium to heal, then eventually was set free back into the Zahhab Region, but has been sighted again...
How to Befriend it
During the last part of the "Best the Best Trainer" quest, the player will notice a report marked "Orca in the open sea."
The player will go diving with Hayako and then head out to the open ocean, around H-7. After focusing on the orca, a cutscene will then show the orca playing.
Then, the player will go back to the Open Sea in Zahhab Region, this time with Hayako, and discover this orca again, and it will recognize Hayako, but not be that kind to your diver.
Then, it's revealed the orca likes floating objects, so the diver will pull out the plastic floating toy and give it to the orca and befriend it.