Ultimate Skill

Ultimate Skills [, ] are evolved skills that are nearly impossible to obtain. Any beings (human, demi-human, monster or demon) can obtain them.

The specific requirements to obtain an Ultimate skill are quite vague. However, it seems that those of very high ability are able to develop them. The majority of Ultimate skill users are quite old (hundreds of years old). The younger Ultimate skill users developed them once becoming a True Demon Lord. An ultimate skill strength is such that it must be defended against with another Ultimate Skill/Ultimate Gift.

A normal human’s body can’t handle the burdens of an ultimate skill’s energy. Under normal circumstances, awakening is impossible. That’s probably why the modified body of an “Otherworlder” is needed. But, at the end of one’s training people will “Evolve”. Their race aside, there certainly is a change. In other words, from a human to a sage.

Ultimate skills are able to be bestowed upon by one's master, but in a much weaker form, an Ultimate Gift.

Types
Currently, the only officially used terms for the types of Ultimate Skills are the Sin Series and Virtue Series. However, Ultimate Skills can be classified as such:

King Series (unofficial)
The King/Lord Series is the default type of Ultimate Skill an individual gets whenever they get one. Whether that is by their Unique Skill evolving or the individual experiencing a reincarnation into a far stronger being.

Naturally, they vary in strength.

The only exception to this type of Ultimate Skill is Sandalphon the Executioner.

Sin Series and Virtue Series (official)
The Sin and Virtue Series Ultimate Skills are the highest tier Ultimate Skills among all of the King Series.

They are based off of the Seven Deadly Sins and the Seven Virtues.

God Series (unofficial)
These are by far the strongest type of Ultimate Skills. They are attained by fusing two or more Sin and Virtue Series Ultimate Skills, by Ciel's skill upgrading abilities, or by bringing one's Sin or Virtue Ultimate Skill to the pinnacle of its usage.

Known God Series Ultimate Skills are:
 * Abyss God Nodens (used by Guy Crimson)
 * Flame God Cthugha (used by Velgrynd)
 * Ice God Cthulhu (used by Velzado)
 * Space-Time God Yog Sothoth Hortz (used by Chloe O’Bell)
 * Void God Azathoth (used by Rimuru Tempest)