Little known fact about Aun'shi.

Aun'shi was denied his much-deserved retirement and sent on an expedition to find out what happened to Farsight. His expedition reached Arthas Moloch and during their survey of the planet, they were attacked by the Drukhari.
Aun'shi stepped up to protect a group of Earth Caste against a trio of Drukhari slavers and their beastly pets. To the surprise of the Drukhari, Aun'shi matched their speed and held them back. However, during the battle, Aun'shi was wounded by a poisoned blade. The poison slowed him down and filled him with agony but he fought on still with the poise of a calm silent warrior until the poison weakened him enough for the Drukhari to capture him.

He was taken to the Dark City where he would become a beloved legend to the Drukhari. They named him the "Fighting Blue Man".  (Check the picture).

Aun'shi would eventually refuse to fight anymore for the amusement of the Drukhari. In response, the Drukhari threw the same Earth Caste from before into the arena and released beasts within it. Aun'shi leaped to action and saved his fellow T'au.

Aun'shi was returned to his hexcage afterward with the T'au he saved alongside him. He vowed to himself that one day, somehow, he would bring the Drukhari to justice for their vile barbarity. To his fellow T'au prisoners, he vowed that, by his duty as an Ethereal, he would always lead and protect them.

The short story doesn't explain how. No source in 40K does! But Aun'shi somehow escaped the Dark City and managed to reach the Farsight Enclaves. He is the only Ethereal allowed to enter the Enclaves.