Quicksword

The Quick Sword (also called Flash Sword) is the signature technique of the Organization's former No.3 Irene. This is performed by releasing excessive Yoki in one arm so that the strength and the speed strongly increase there. The user then unleashes a massive amount of powerful slashing attacks that can tear an opponent to pieces. Irene (and eventually Clare) mastered this technique to such a level that the strikes couldn't be tracked with the naked eye. ( Irene didn't appear to even draw her sword when using the technique, as show when she was fighting Teresa; she appeared to be simply standing there, completely still, while the technique decimated the room they were in.)

Irene described it as Awakening one arm alone. Because of the chaotic nature of Awakening, a massive amount of concentration is required to maintain control over the appendage and to keep the user from fully Awakening. Especially given the natural instinct to release Yoki throughout the entire body, Irene stressed this while training Clare.

It is first seen at the execution of Teresa (vs. Priscilla, Irene, Noel, Sophia). After the fight between Ophelia and Clare, Irene intervened and saved Clare. Later Irene taught Clare this technique so she could remain formidable after losing her sword arm. While training Irene explains that the Quick Sword can only be used by a calm nature and Clare couldn't use it very well because she has always a fire burning inside her heart even when Clare shows herself as a calm and emotionless Claymore.