After Tidus is taken from Zanarkand by Sin, he ends up in Baaj Temple. A group of Al Bhed arrive and save him from a monster attack, but soon turn against him. To be allowed to stay, Tidus must help the Al Bhed in exploring the underwater ruins, and he begins the exploration with an Al Bhed girl called Rikku. Inside the airship, they fight and defeat the Tros. After defeating the octopus fiend, they succeed in salvaging the airship.
"Underwater Ruins" is played inside the Underwater Ruins.