Inherent Skill (インヒューレントスキル Inhyūrento Sukiru), shortened to IS (IS Ai Esu) and sometimes rendered in kanji as Inherent Fixed Skill (先天固有技能), is a specialization of each Number, ranging from passive abilities, e.g. Uno's information processing skills, to purely combat applications, e.g. Cinque's Rumble Detonator. Although the IS may appear like magic, it is not, as it is fixed and cannot be learned or otherwise directly transferred to anyone but its owner because it is intricately tied to a particular Number's cyborg frame.
The "Inherent Magic/Spell" used by Subaru and Ginga Nakajima, Wing Road, is similar to an IS but is mana-driven. Their Devices, Mach Caliber and Blitz Caliber, have been modified to augment this spell and even cast it on their own, but this required complex calibration beforehand.
Full list of known Inherent Skills and derived abilities:
|Oscillating Breaker||Subaru Nakajima||Attack||Shooting|
|Oscillating Knuckle||Subaru Nakajima||Attack||Melee|
|Prisoner Box||Otto||Force field||Area|
|Revolver Shoot||Subaru Nakajima||Attack||Shooting|
|Twin Blades (spell)||Deed||Attack||Energy blade|