Unique Skills (ユニークスキル Yunīkusukiru) are Skills that, as the name suggests, are Unique and only exist one at a time. They are the next stage of Skills after Extra Skills. Unique Skills are described to be the "shape of the mind."
Characteristics of Unique Skills
Unique Skills usually are composed of multiple Sub-Skills which might be Common Skills or Extra Skills, or have a sub-Skill that is unique to that specific Unique Skill.
There are conditions that need to be met to obtain Unique Skills. One of the conditions is that the bearer must have desires. Someone who has no desires or strong feelings can't obtain a Unique Skill, as Unique Skills are the shape of the mind. Even if someone successfully steals a Unique Skill from someone else, if its nature doesn't fit the new user, the potency of the Skill will be greatly lowered. Another condition is that the user needs to have a certain amount of Magicules available, as obtaining a Unique Skill causes one to permanently lose Magicules.
It's for that reason that various Human nations are summoning Otherworlders, as Otherworlders, when crossing over between worlds, go through a fundamental change due to going from a physical world to a mixed physical and spiritual world, and in the process often gain a Magicule-compatible body that is more likely to obtain Skills than Inhabitant Humans. Summoned Otherworlders in particular always obtain a Unique Skill when summoned - which is also the reason why the nations usually put a slavery curse on their Summons, as they might otherwise kill their summoners in retaliation and escape due to their unpredictable Unique Skills.
Known Unique Skills
Main Topic: Unique Skill List