Mysterious Heroine X



  • True Name: Mysterious Heroine X
  • Class: Assassin (insists she is a Saber)
  • Source: 2013 April Fools’
  • Region: Servant World
  • Gender: Female
  • Alignment: Chaotic Good
  • Height: 154cm
  • Weight: 42kg


  • Character Creator: Kinoko Nasu
  • Original Character Design: Takashi Takeuchi
  • Character Illustrator: BUNBUN
  • Character Voice: Ayako Kawasumi
  • Appearance in Main Works: Back Alley Satsuki – 12 Heroines Sanctuary Arc, Fate/Grand Order


Magical PowerB
Noble PhantasmA++

Class Skills

Cosmo Reactor: [A]

A reactor that’s cosmic, it’s allowed only to the shining Saber.
The reactor reacts to many things. Like the plot, for example.

Riding: [EX]

Talent for riding. She can’t manage most mounts and vehicles, but she is amazingly effective when it comes to piloting junk spaceships. To the point that she can make a ship with no warp function warp.

Presence Concealment: [-]

Are you implying Sabers have that!?
(It’s actually ranked EX, but it’s sealed since she completely denies it)

Personal Skills

Back-up Fire: [EX]

Using a mysterious communication device, she can have Du Stallion II automatically perform back-up fire.
In a duel between knights, there’s no such thing as dirty trucks and underhanded tictacs.

Instinct: [C+]

Considerably downgraded compared to the normal Arthuria, but it ranks itself up to A-Rank Instinct for anti-Saber purposes only.

Galactic Meteor Sword: [C]

A power given to Saber that can destroy even stars.
Also known as the sword that absolutely kills Sabers.
Since it’s super-effective against Sabers, wouldn’t you agree that this makes her the greatest Saber of all?

Noble Phantasm(s)

Himitsucalibur (Nameless Victory Sword)

  • Rank: A+
  • Type: Anti-Unit
  • Range: 1-99
  • Max. Targets: 1 person

Holy swords that boast a tremendous power against Sabers.
They don’t launch beams, but they are covered in them. Also, they make this neat low-register woooooom woooooooom sound every time she swings them.
… Hey, I’m sure I’ve heard that somewhere before.
Dual-wielding swords of opposite attributes requires a tremendous power management. That goes to show how out of the ordinary Heroine X is.
It even seems like light and darkness are strongest when they mingle.



First person pronoun: watashi
Second person pronoun: anata/ omae
Third person pronoun: kare/ kanojo


A personality like Arthuria-san but without any of the seriousness.
She is overly serious, driven, and absolutely unforgiving of evil.
Because she also got a boost to her quick temper, she was turned into the foolhardy chairman type of character. This honesty makes her easily deceived.
She exceedingly loves, hates, and grieves over Sabers.
She’s adamant that she is the only Saber the world needs and makes a point that some underhanded trickery is necessary for that purpose, but due to her innate goodness, she is less than successful with this. No matter how she spins it, she can’t turn into a villain.

Attitude Towards Master

“I pray that all Sabers besides me perish.
Another desirable option is that they stop calling themselves Sabers and get some other classification, like maybe Attacker or Swordsman.”

As her base is still who she is, she will never have a bad attitude towards her Master.
However, given the opportunity, she will try to unlock the Sabers other than herself.

Dialogue Examples

“Die, Sabers other than me.”

“No one becomes a Saber overnight! Remember to sleep early, wake up, always eat all of your vegetables, and take breaks whenever necessary!”

“Look, Master, this is my new form! Defeating the Arthuria-type Sabers is now something too small and meaningless for me to mention! My new objective is to become the strongest Saber to be of use to you!”

Character Image

It all begins with Mysterious Heroine X appearing for April Fool’s in April 1st, 2013.
The blue scarf, the hat, the ahoge piercing through it, the visibly dangerous adorned holy sword.
Her true identity is Arthuria Pendragon.
The most notorious Main Heroine… she was supposed to be. Feeling threatened by rise of Red Saber and Black Saber, she swore to eradicate all Sabers!
Going by that logic, her Class was set as Assassin.

She works as a Main Heroine in a newly introduced mysterious world, the Servant Universe.
Since evil Servants can go as wild as they want, American-style, on parallel worlds in the Servant Universe, the Mysterious Heroine X hides her identity with her hat and scarf and fiercely fights night and day against the world destruction-scheming Captain☆Nikola.
Also, since this world has a condition where the Villain Servants don’t die, they are only sent to jail, from where they can escape whenever they want to joyfully and cheerfully go back to doing their evil works.
Sometimes they do die, are killed, make someone die, switch to the heroes’ side or become zombies.
It’s a nonsense land where all characters of all worlds are bound to hero/villain character roles that get reset when they go back to their home place, making their character development start back from scratch.

In Fate/Grand Order, the number of Sabers increased exponentially.
She says this increasingly fills her with desire to kill and that they are enemies worthy of her holy sword or some crap like that.

The Saber Class

Sabertei Must Be Destroyed.

Arthuria Lily

Too soft! (No self-awareness about her own softness)

Mysterious Sailor X

… Huh? Who are you? Someone from Episode II perhaps?

Comment from the Illustrator

She was a character from one of Type-Moon-san’s April Fools’ projects and one I always loved, so I gladly accepted the job, but her design was already complete, so when it came to make alternate designs, whenever I put something in or took something out, it felt wrong… My only option was to think outside of the box, ready to be scolded for it… and so I sent that final form and got the OK against my expectation. But in the end… who even is she…? (sophisticated beauty) (BUNBUN)

Material Images

(Lib will add after publish)