|This page contains spoilers for:||The Flight of the Eisenstein (Novel)|
According to Captains Typhon and Grulgor, Arin was one of many human Aspirants to the Death Guard, who failed miserably but could not bring himself to end his own life. These Captains, however, were known for their disdain of non-Astartes humans.
As Captain of the 7th Company, Garro was traditionally entitled to an equerry, and chose Arin, whose duties included overseeing the maintenance and repair of Garro's Power Armour and his sword, Libertas. Garro valued Arin's service, and relied on his discretion. In particular, he asked Arin to keep his ears open when Garro discovered the existence of secret lodges forming among the Death Guard's elite warriors.
Arin later met a heroic end aboard the frigate Eisenstein over Isstvan III. While Ignatius Grulgor prepared to bomb the surface of the world with Life Eater virus capsules, Garro tried to stop him. When Grulgor tried to shoot Garro, Kaleb fired at Grulgor's gun with his own, knocking it off target. Grulgor responded by stabbing Arin with a combat knife, but the stray bolter round hit one of the Life-Eater capsules, releasing the deadly virus.
Arin threw himself onto the emergency release switch, sealing himself, Grulgor and the other Traitor Astartes inside the launch bay, to protect Garro and his company. As he did so, he shouted to his Captain that Garro was "of purpose," and that he must survive, no matter what. After he died, Garro found the Lectitio Divinitatus in Arin's belongings, realizing that he was a secret follower of the cult of the deified Emperor.