After the Archadian occupation, he and Captain Azelas led an assault on Nalbina Fortress in an attempt to save the king, only to be captured by Imperial forces. As part of Vayne's plot to frame Basch, Noah, now Gabranth, posed as his brother and slew the Dalmascan king and later Vaan's older brother, Reks, who witnessed the crime. As a result, Basch is regarded by the Dalmascans as a traitor, and was stated to have been executed by Marquis Ondore. In reality, Basch was imprisoned alive in the Nalbina Dungeons by Vayne as a means of ensuring Ondore remains loyal to the Empire - if Ondore betrayed the Empire, all Vayne would have to do would be to announce Basch's continued survival to destroy the Marquis' credibility.
He was eventually freed by Vaan, Balthier, and Fran who were trying to escape Nalbina dungeons. Though all three were initially suspicious of him, Vaan in particular, the party did catch a look at Gabranth's face, lending credibility to Basch's story that he had been framed. After the escape, he decided to protect Ashe and help the resistance, in spite of his past failures. He remained loyal as well, even through such events as Vossler's betrayal. It was Basch's devotion to honor despite everything else that most puzzled his twin, Gabranth, and was the source of the division between them. Eventually coming to respect Basch's viewpoint more than his own, Gabranth sought to redeem himself and remained true to his own devotion to Larsa Solidor, helping his brother and Ashe defeat Vayne on the Bahamut. After the battle, as Noah was dying, he asked his brother to protect Larsa in his place to ensure peace. Because common belief of Captain Ronsenberg being dead, Basch easily took over his brother's stead as "Judge Magister Gabranth" to be the protector of the new Emperor Larsa Solidor.
In the sequel Final Fantasy XII : Revenant Wings, though a Judge on false pretenses, Basch intends to protect the peace he and the others obtained when he journeyed as Larsa's representative to deal with the Judge of Wings. Basch's presence affects Kytes, who wishes to be like him someday
Article Source : Wikipedia