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 it 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 status information pertaining to 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 helmet can be removed at will when utilized in battle, splitting in two down the middle and merging into her armor. Removal of the helmet required for the use of Clarent Blood Arthur, so she must reveal her face should she wish to utilize it.
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5
 Fate/Apocrypha material - STATUS: Saber of Red, p.032-033
Master: Kairi Sisigou
True name: Mordred
Alignment: Chaotic Neutral
Noble Phantasm: A
■ Magic Resistance: B
Cancel spells with a chant below three verses. Even if targeted by High-Thaumaturgy and Greater Rituals, it is difficult for her to be affected.
■ Riding: B
Most vehicles can be handled with above average skill. However, cannot ride the likes of Phantasm Races such as Monstrous Beasts.
■ Instinct: B
During battle one is able to always feel the optimal course.
Visual and auditory obstacles are halved.
■ Mana Burst: A
Weapons and body are infused with magical energy, this instantaneous release elevates ability. In other words, magical energy as jet propulsion. With this is able to fight equally with the King of Knights.
■ Battle Continuation : B
Doesn't know when to give up. Did not give up even when pierced with a Holy Spear and ended up giving the King of Knights a mortal wound.
■ Charisma : C-
Natural army commanding talent. During team battles one's team's abilities are elevated. A rare skill.
Mordred's charisma fully shows itself during during rebellion.
■ Secret of Pedigree: Helm of Hidden Infidelity
Type: Anti-Unit (Self) Noble Phantasm
Range: 1 Person
Maximum number of targets: 1 Person
The helmet her mother Morgan gave to her along with the words "You must not remove." Within the Status, personal skills, Noble Phantasm and anything connected to the True Name is masked. However when Clarent: Radiant and Brilliant Royal Sword is released, the helmet must be removed.
■ Clarent: Radiant and Brilliant Royal Sword
Type: Anti-Unit Noble Phantasm
Maximum number of targets: 1 Person
The sword denoting the right of succession of the throne that was stored in King Arthur's armory. It is described as "more dazzling than any silver, and is a treasured sword with worth excelling or at least not inferior to "The Golden Sword of Promised Victory." Because Mordred stole the sword without acknowledgement, the rank is lower than the original.
■ Clarent Blood Arthur: Rebellion Against My Beautiful Father
Type: Anti-Army Noble Phantasm
Maximum number of targets: 800 People
Clarent's full power released form. Original was an ornate, sparkling white silver sword, but when invoked it is dyed with dark red blood and warps into an unsightly form. The blade is clad in wanton hatred and fired. A demonic sword of calamity.
- ↑ 2.0 2.1
 Fate/Apocrypha material - Encyclopedia: Helm of Hidden Infidelity [Noble Phantasm], p.169 [T]
Helm of Hidden Infidelity [Noble Phantasm]
Secret of Pedigree. The Noble Phantasm of Saber of Red, Mordred. She hid her face with a helmet given to her as a set with a suit of armor by Morgan in order to prevent King Arthur and his subordinates from learning of her true identity.
It’s a little like a simplified version of “For Someone’s Glory: Not For One’s Own Glory” from “Fate/Zero”. The condition to negate the effects of this Noble Phantasm is solely the act of her removing her helmet on the battlefield, so it will continue to hide her stats even if she walks around normally with her face unhidden. I understand it seems like a bit of a lame excuse, but walking through the streets in a suit of armor only works in a Fantasy RPG world, so please bear with it.
Perhaps due to having being enchanted by Morgan, both the helmet and armor are quite sturdy in terms of defense as well. Furthermore, “Clarent Blood Arthur: Rebellion Against My Beautiful Father” cannot be used until the helmet is removed. As a result, Mordred keeps it almost always removed after she first takes it off the time.
This is a bit of a digression, but the helmet isn’t placed down anywhere when it’s off, but instead is inserted into the armor (the reverse is also possible). I found the scene where the protagonist of a certain Sci-Fi Horror TPS Game equipped their helmet to be really cool, so I fervently requested it of Konoe-san (TL note: the illustrator). Even if the author was satisfied with it, it was probably a huge annoyance to him. Sorry.