Secret of Pedigree: Helm of Hidden Infidelity (不貞隠しの兜, Futei Kakushi no Kabuto?) is the helmet of Mordred given to her by Morgan along with the words "You must not remove", told to wear at all times in order to keep her identity and lineage a secret. Manifesting from the fact that it was never once removed in public until her final fight with King Arthur, it hides certain sections of her parameters, even from her own Master, making it hard to discern even her gender when coupled with her full body armor. Her basic parameters and class skills can be seen, but her personality and true name as a Heroic Spirit, innate skills, and data on her Noble Phantasms are hidden and cannot be read. Masking anything related to her true name, Darnic Prestone Yggdmillennia has a feeling that he can recognize her abilities and the design of her sword, but it seems like he is prevented from recollecting the information.
Her statistics and data are only released upon "taking off" the helmet while it is "set" in her armor. She can remove both the helmet and her armor and clothe herself in modern attire while still hiding her identity. The concealment will continue to function even without the helmet so long as she does not hold her weapon. The helm can be removed at will when utilized in battle, splitting in two down the middle and merging into her armor. This is required for the use of Clarent Blood Arthur, so she must reveal her face should she wish to utilize it.