WN/Sin Series

Sin Series Ultimate Skills are a skill that are based around the seven deadly sins. They are considered to be the most power of the Ultimate Skills that an individual can obtain, only inferior to the ones having the label 'God' in them.

Unlike other Ultimate Skills, the Sin Series have worldwide significance, as when one accumulates all seven of them, there is a bonus effect that releases the racial limits of the Demons, which would be to open up their natural evolution to stages beyond the Arch Demon.

Although unclear what it is meant by 'accumulates' but it can be conjectured that the individual needs to be of demonic affiliations and have people who are part of the individual's 'faction'. In the story, such an individual would be Guy Crimson representing the Demon's faction, and similarly, Rudra Nam Ul Nasca representing the opposing Angel's faction.

The Sin Series Ultimate Skills are a subset of a broader series called the Demon Series. Unlike the Angel Series where Justice King Michael has the ability to control everyone with an Angel Series Ultimate Skill, no such ruling skill has been mentioned about the Demon Series. However, it may be assumed that a similar ability is given to Prideful King Lucifer since Guy had it, and Rudra had Michael.

Also, apart from the Sin Series, there has been no other Ultimate Skills that has been explicitly mentioned to be of the Demon Series. Speculatively, however, the likely candidates are: The seven deadly sins and their correlated Ultimate Skill are as follows:
 * Hell King Belial
 * Illusion King Mephisto