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). Although it is possible to quickly acquire an Ultimate Skill through becoming a True Demon King, this is not guaranteed. In order to acquire such a Skill, great willpower and control is needed. 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 why the modified body of an “Otherworlder” or similar physiques 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.

It is also possible to bestow skills close to Ultimate skills by one's master if he holds an Ultimate Skill by himself, but in a much weaker form, known as Ultimate Gift.

In Chapter 190 of the web novel, as Rimuru pondered about the nature and existence of skills, unique skills and ultimate skills, he explained how even if some (unique) skills can be grouped together because of their similarity, none are identical. He also explained that it's possible for skills with the same name to have different performances and rules.

As such, the name of a unique skill (and also an ultimate skill) can be thought to be a 'label' given to a 'container' that has the probabilities of obtaining numerous effects. This can be thought of as a game skill capable of exhibiting 10 effects total, but the player has only 6 while the other 4 are grayed out or invisible. An example of this would be Rimuru's Ultimate Skill Uriel and Chloe's Ultimate Skill Sariel both evolving from and having the properties of Infinite Prison.

Another example would be Carrera's Abaddon that added Sandalphon's effect "Divine Edge" to itself, meaning that Extinction King Abaddon already had the "aptitude" for Divine Edge but simply didn't obtain/unlock it until that time.

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 an evolution 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)