WN/Virtue Series

Virtue Series Ultimate Skills are a skill that are based around the seven virtues. Although their definition is not as clear as the Seven Deadly Sins, the author seems to be using words analogous to both the Four Cardinal Virtues and Three Theological Virtues, and also from the second set of Seven Heavenly Virtues that are meant to oppose the Seven Deadly Sins.

They are considered to be the most powerful of the skills that an Angel or Hero type can obtain. When one accumulates all seven of them there is a bonus that released racial limits of angels and/or angelic beings i.e. being freed from command and becoming independent individuals.

The Virtue Series of Ultimate Skills are a subset of a broader series called Angel Series. Michael has the ability to completely dominate over anyone with an Angel Series Ultimate Skill, which was how Manas: Lucia was able to control Dino's (who had Fallen King Luciel) actions in favor of Manas:Velda even if he knew that Velda wasn't actually Veldanava. The only reason he was later able to break free was that he also had Slothful King Belphegor, which is a Sin Series, or Demon Series, Ultimate Skill.

As stated by Diablo, the Angel Series Skills possessed the most powerful defensive abilities of all the Ultimate Skills series sets.

Also, apart from the Virtue Series, there has been no other Ultimate Skills that has been explicitly mentioned to be of the Angel Series. Speculative, however, the likely candidates are:

Officially, only Sky King Luciel (and hence also Fallen King Lucifel) has been confirmed to be an Angel Series Ultimate Skill. Speculatively, other Angel Series candidates are:
 * Melchizedek
 * Sandalphon the Executioner
 * Sky King Luciel (and hence also Fallen King Luciel)