The Seven Deadly Sins... Pride, Wrath, Greed, Envy, Lust, Gluttony, and Sloth; they have been around since the beginning of time. Unbeknownst to those outside of Hell, there is a physical embodiment for each of these sins. Though they are considered spiritual beings, they can be seen by ordinary humans, yet they and their weapons can interact with Shinigami, Arrancar, and the like. They are extremely powerful, and can traverse freely between Hell and the other dimensions.
All sins have a special passive ability that does not have to be listed in the technique list. This ability dictates that a Sin cannot die indefinitely unless stabbed in the heart. If they die of any other cause, they will simply be sent to Hell, where they will be require to go through a trial. Until said trial is completed and approved, they cannot leave Hell.