A spin-off series from the hit manga Gangsta that tells the backstory of Marco Adriano.
 

The man named Marco Adriano is a loyal and beloved member of the Cristiano Family, helping them protect the persecuted Twilight population in the city of Ergastulum. But he was once a boy codenamed “Spas,” raised as a Hunter and assigned to the Destroyers Second Group for a single purpose: to track down and kill Twilights.

Killing is all Spas has ever known, and he does it without doubt or remorse. Taught to believe he’s ridding the world of monsters, he sees the extermination of the Twilights as a necessary step toward making Ergastulum a safer place. Until the day when he’s forced to confront the horrifying truth that the real monster might be…him.