A Tanith born trooper originally of Adare's/Raglon's platoon but later part of K Company under Captain 'Shoggy' Domor. Costin was one of the Tanith First's most infamous drinkers, known even by reputation only to many who'd never engaged him personally, and was described as ruddy-faced drunkard who would often brew his own sacra to keep up with a habit that his rations only couldn't cover.
First mentioned in Ghostmaker having broken his shin in a stupor induced from inhaling paint thinners after already using up his sacra rations but wasn't in the spotlight again until Straight Silver when, unsurprisingly drunk, on an incursion into the Shadik's trenches he took a sip from a sacra flask and the reflected light was noticed by an enemy sentry. Almost half of Raglon's unit lost their lives, including Costin's good friend Scout-Trooper Suth, and Costin came to within spitting distance of being executed by Gaunt himself were it not for the pleading of both Raglon and Dorden. Following this gave incident Costin initially cleaned up his act and was seen taking the helm of an bold rearguard action in Sabbat Martyr then later on in Blood Pact reading a sermon at Zwiel's services.
Sadly by the time of Salvation's Reach Costin has fallen to his alcoholism once more. And if this wasn't bad enough he'd also became involved in Captain Meryn's insidious fraud scheme of claiming the pensions of deceased or even fictional war-widows. When the plot was almost uncovered and Costin riled by Major Rawne it was decided by Meryn, and co-conspiritor Sergeant Gendler, that Costin was a risky loose-end and to silence him the two left him (and four other troopers) cut-off and stranded in the face of a Loxatl force where all five were butchered.