Sin

 is a gameplay mechanic in Dark Souls.

Description
The player's Sin value determines how likely it is for a member of the Blade of the Darkmoon covenant to invade the player. Once a player obtains Sin, their username is entered into the Book of the Guilty, and will remain there until the player's Sin value decreases to zero.

Obtaining Sin
There are two ways a player obtains Sin. One is by invading other players and killing them, unless the player is invading as a member of the Blade of the Darkmoon covenant. If the invaded player chooses to use an Indictment, the invader's Sin value increases by one.

The second way is to kill a friendly NPC, such as Solaire or Lautrec (before he goes to Anor Londo). This increases the player's Sin value by one also.

Removing Sin
Sin can also be removed in two ways. One way is to absolve Sins at Oswald of Carim in the Undead Parish. In order to absolve their Sins, the player must make a payment of souls to Oswald. The cost of absolution is calculated by multiplying the player's Sin value by 2,000.

The second is to be invaded by members of the Blade of the Darkmoon covenant enough times for their Sin value to be negated. Every time the player is defeated by a Blue Phantom, their Sin is reduced by one.