Terra and Aqua have known each other for a very long time, probably since they were children. They are both from the Land of Departure and trained under Master Eraqus. Both shared the same dream of becoming a keyblade master and looked after Ventus together after he arrived. Eventually, the two had their Mark of Mastery exam together. They were forced to spar and only Aqua passed because Terra had the darkness inside of him. However, both were still sent on a mission to investigate the unversed in other worlds and find Xehanort. However, Eraqus was worried about Terra and ordered Aqua to bring him back if need be.
As the two traveled to other worlds, they briefly ran into each other at the Castle of Dreams. Terra told Aqua what he learned from Cinderella and Aqua showed that she had faith in Terra. The trio later reunited at Radiant Garden and fought a giant unversed together. Terra and Aqua laughed as Ven gave them passes to Disney Town but tensions soon grew between them. He learned that Aqua was keeping an eye on him per orders of Master Eraqus so he distanced himself from her.
Aqua eventually arrived at the Mysterious Tower and learned from Yen Sid that Master Eraqus was killed. He explained that Master Xehanort and Terra were both possible suspects and she did not want to believe that Terra could have killed him. They were later reunited in the Keyblade Graveyard and Aqua asked Terra about it. Terra admitted that he helped Xehanort kill Eraqus and how he was only trying to protect Ventus. The three then faced off against Master Xehanort and Vanitas. At one point, Terra was bombarded by keyblades midair so Aqua cast reflect on him from a distance.
After the battle, Master Xehanort possessed Terra and the two fought for dominance over the latter's body. Meanwhile, Aqua took care of a comatose Ventus and believed that both she and Terra could help him wake up some day. She later found Terra-Xehanort (possessed Terra) in the Radiant Garden and fought him. However, the battle was interrupted and Terra-Xehanort fell into the Realm of Darkness. Aqua dove in to save him but realized that they could not make it out of the portal. She sacrificed herself for him, sending her armor and keyblade back to the Realm of Light with him. Aqua is now trapped inside the Realm of Darkness and hopes that she can see her best friends again. Terra-Xehanort was found by Ansem the Wise and became one of his apprentices, Apprentice Xehanort.
Terraqua is a very popular Kingdom Hearts ship and is probably the most popular ship involving Terra and Aqua. This ship got an overwhelming amount of support after Kingdom Hearts Birth by Sleep as the two were often seen working together and have known each other longer than Ven. A lot fans also pointed out the fact Aqua sacrificed herself to save Terra from being stuck in the Realm of Darkness.
- Ventus was told to give the two extra passes for Disney Town to his parents and ended up giving them to Terra and Aqua. Many see this as Ven seeing Terra and Aqua as his parents.