After the decimation of Tidus' hometown of Zanarkand is concluded, he'll be alone in the watery ruins outside of Baaj Temple. Swim around the area to explore a bit and build up your characters' experience. If Tidus swims to the left, he can find an Al Bhed Compilation Sphere (useless for the time being). All the way to the right he can find a blue note written in Al Bhed, which is a simple substitution cipher (i.e. all the letters of the alphabet have been switched), which states "In the land where balls of light, illuminate the blackest night, with Macalania behind the fourth pillar you sight, look not on the left but on the right." Right behind it and actually presently worthwhile is a treasure chest, containing 200 Gil. Just head North (proceed in the direction indicated by the red flashing pointer) from there until he can find some dry land and climb up upon it. Use the save sphere, which you find here. Next go to the left and find a chest containing a Hi-Potion. Go back toward the save sphere and then just continue upward until he triggers another cut scene, after which the path beneath his feet crumbles and falls beneath him. Swim forward a little ways until the Sahagins pop out and a battle ensues. They're just an annoyance to get in your party's way before the upcoming battle with Geosgaeno. All your group has to do is destroy two of the three to initiate the game's sole bloody scene, where the gigantic Geosgaeno chews and then spits out the remaining Sahagin. Don't bother attacking it unless you want to, but rather just keep trying to flee until it actually lets your party do so, because it's way to powerful for your group at this point in the game. They'll be back here much later in the game to take it on.

Tidus and you now get a little peace and quiet. Save your game at the save sphere inside the main room. Next have Tidus walk to the center and examine the remains of a fire. Tidus is cold and wants to rekindle the fire. You now have to have him find the proper materials for rebuilding a new fire. Enter the door closest to the dormant fire to find a chest. Examine it to obtain the Flint. Take the passage to the right and head upstairs. Skip around the broken pillars until he finds another treasure chest containing a Hi-Potion. Return to the main room, and proceed through the only other door, which can be opened. Continue up the stairway, hugging the right wall all the way up or you'll get to try it again. When the "Examine" signal appears, do so to receive the Withered Bouquet. Return downstairs and grab the Ether potion from the chest, than return to the main room and examine the fire remnants to trigger a cut scene, wherein something freaky is running around and Tidus' newly lit fire is extinguished. He now gets to do battle with Klikk.

After your two characters defeat it, watch the cut scene where Rikku surprisingly knocks Tidus unconscious. The next thing you know, you find that Tidus is on some sort of vessel and apparently a captive of the Al Bhed.