Invisible Air

A sorcery, rather than a Noble Phantasm, which compresses and gyrates the air around Saber's blade. The circulation of wind distorts the refraction of light, inducing an illusion of ethereality. This property makes it difficult for opponents to parry lunges and thrusts from Saber, for they cannot discern the length or width of the blade. Furthermore, the pressurized air can be offensively expelled once in the form of an intense gust. Although quite useful in combat, the primary purpose of Invisible Air is to conceal Saber's identity, for her true Noble Phantasm is very famous and easily recognizable.

Additional source: Fate/Stay Night game translation v1.0a by Mirror Moon