He lived in Destiny Islands with Ana and Gabriel until they decided to venture to The World That Never Was. There they were attacked by a Twilight Thorn. Ana and Gabriel were defeated and turned into a Heartless. Nathan, terrified and worried for his friends, fortunately knew that there was a chance that they were turned into Nobodies, so he fled to Twilight Town, hoping to find them there. Luckily he did.
They went to the nearby abandoned Mansion and trained there for two years. They then departed to Yen Sid's Tower, where Xirbealg and Axna became the great Wizard's apprentice. Yen Sid gave them a special mission and a team at their disposal called Organization XXI. They were to become keepers of the peace, but Nathan, feeling that he wasn't powerful enough to be a great asset, declined membership, instead telling his friends that he was just going to help them however he could. When Xirbealg was confronted by Sephiroth Nathan was coming out of the mansion in time to see Sephiroth disappear. He then trains with Xirbealg until he is so injured that he goes berserk and summons a keyblade and almost kills him.
Xirbealg realizes he still feels emotions and misses Axna. Axna returns to see the group and is convinced by Nathan and Xirbealg to stay. She reveals to have gotten stronger and trains with the rest of the organization in an all out battle to see who is strongest and for practice. In the end it was just the three friends, Xirbealg, Axna, and Nathan. Axna and Xirbealg took out Nathan together by using their group limit break, and then the two were tied and collapsed side by side and hand in hand.
A New Enemy... Or Friend?
Xirbealg and Nathan go on a recon mission to Agrabah and encounter Madara's apprentice, Sasuke. Nathan decides to test his newly acquired dark-element abilities and summons a dark corridor to send them to the dark realm. Nathan asks Xirbealg to stay out of the fight and he does until Sasuke summons a dark keyblade much like the one that Riku used while possessed by Xehanort's heartless. At this moment he realizes that Sasuke's appearance and fighting style are very similar to his own. He sees Sasuke's sharingan and tells Nathan to go back to Twilight Town as he gives him a potion. Nathan unwillingly does as he is told.
On the way to Hollow Bastion the Organization is attacked by Akatsuki. Xirbealg and Nathan team up with Leon and beat Sephiroth who's remnants then turn into Cloud. Sasuke kills Itachi and Axna destroys Genesis. After a huge battle only Madara remains on akatsuki's side but Xirbealg and Axna reach their limit and Xirbealg plummets to his death. Before he hits the ground Axna cries and as her tears touch Xirbealg it is revealed that Ana's heart was within Xirbealg's body and Gabriel's heart was in Axna's body. They both become whole once again.
Main article: Nathan/Abilities
Like Axna he wields a keyblade and the power of light as well as various staffs and swords. He controls the enemies that appear in the virtual town through his computer and uses blizzard magic often.