Why Is Basch Kept Alive?
The main reason why Vayne keeps Basch alive is to silence Marquis Ondore. However, another reason is to extract information about the whereabouts of the Dusk Shard, which Vayne failed to obtain for two years. But Emperor Gramis, unaware that Vayne had been after the nethicite way back then, becomes suspicious of Vayne’s actions—particularly the fact that he’s letting Basch live. Gramis orders his confidant Judge Gabranth to investigate Vayne’s true motif. Gabranth's visit to Basch’s oubliette is thus carried out under Gramis’s directive. At the same time, Gabranth has a personal motive: a desire to know why his resented brother has been allowed to live.
Though his words are meant to dig Vayne’s intentions in keeping Basch alive, they also carry an intense hatred, as if to say, “Why is someone like you still breathing?
Can’t He Just Ask Vayne?
Though Gabranth serves under Vayne, Gabranth is secretly investigating him under a covert order from Emperor Gramis. That’s why he can’t directly ask Vayne why Basch is kept alive.
However, Vayne is fully aware that Gabranth is investigating him. Even Gabranth’s meeting with Basch is something Vayne allows deliberately—he hopes Basch might accidentally reveal useful information, such as the whereabouts of the Dusk Shard, and so he lets Gabranth continue his actions unchecked.
Since any meeting with a prisoner requires Vayne’s permission and cannot happen without an escort of imperial soldiers, Gabranth is unable to conceal from Vayne anything he learns during the meeting.
And even if Gabranth were to discover information from Basch that could disadvantage Vayne, there's a high likelihood Emperor Gramis would execute Gabranth to silence him in order to protect House Solidor.
Serving both Vayne and the Emperor, Gabranth stands in an extremely precarious position—he’s constantly at risk of being cut down by either side at any moment.
Source: Final Fantasy XII Ultimania Ω (Omega), 2006, Page 41.

















