To acquire Lulu&;s ultimate weapon, Union
Knight, return to Baaj Temple (where Tidus first woke up) and dive
underwater. Swim towards the doors to the north to fight Geosgaeno. A
strategy for this boss is detailed below, in the section on obtaining
the aeon Anima. After defeating Geosgaeno, search the southern part of
the circular underwater area and look for a treasure chest containing
the weapon.