Ultimate Skill

Ultimate Skill (究極能力) is the evolved form of Unique Skill and the final evolutionary stage of Skills in general.

Ultimate Skill Characteristics
Ultimate skills, as the name implies, gives the wielder ultimate power to control the very laws of nature. The only way to counter an ultimate skill is with another ultimate skill. That is the absolute, unbendable rule of the world.

Skills of this class, normally, may not be shared or copied. Only one individual in the universe may own a skill of this class until its current user is either killed or somehow lost the skill in some way.

Through later volumes, it's revealed that via certain methods, ultimate skills can be imparted to others who have not naturally acquired them, albeit with potentially reduced capabilities. The requirement is that the subject must be a spiritual life-form due to the sheer capacity needed to hold an ultimate skill. The downside of gaining strength this way is the subject is less likely to be attuned to their power given that it wasn't obtained through their desire, meaning they won't get as much out of it as someone who awoken it through their own efforts. This becomes less of an issue the more compatible the subject is to the borrowed power.

Ultimate Skills
Rimuru Tempest:
 * Azathoth, God of Void
 * Shub-Niggurath, Lord of Harvest
 * Raphael, Lord of Wisdom
 * Beelzebuth, Lord of Gluttony
 * Veldora, Lord of Storms
 * Uriel, Lord of Vow

Veldora Tempest:
 * Faust, Lord of Investigation

Luminous Valentine:
 * Asmodeus, Lord of Lust

Yuuki Kagurazaka:
 * Mammon, Lord of Greed

Chloe Aubert:
 * Sariel, Lord of Hope
 * Yog-Sothoth, Lord of Space-Time

Trivia

 * In the story, the characters pronounce Ultimate Skills using only the being they reference and not the entire names used in the wiki and translations. Meaning, it's "Ultimate Skill Beelzebuth" not "Ultimate Skill Gluttonous King Beelzebuth." This is due to the Japanese texts themselves. (See: Furigana and Ruby Characters)