The Sword of Sin along with its sister sword, Sword of Salvation was used by the Order of Purity's Azrael since Geoffrey de Cantonna first donned the Suit of Sorrows after the Crusades. The Sword of Sin was retained by the Order of Purity even after the Sword of Salvation and the Suit of Sorrows was lost to Ra's al Ghul, a long time rival of the Sacred Order of St. Dumas.
The Sword of Sin has to ability to conjure in the mind of a target on the recieving end of the blade all of the sins for which they are guilty or have not attoned for. For this reason, it is Azrael's preffered blade to use. Like it's sister sword, the Sword of Salvation, it is capable of cleaving right through a target without leaving a mark. Used on a target at the same time as the Sword of Sin, it can bring up both the sins & guilt and the reasons behind them in the mind of the target and the wielder. It is often surrounded in an aura of flaming energy.
Both the Sword of Sin and the Sword of Salvation appear to be animate, "speaking" to the bearer.