Disclaimer: I do not own the Fate franchise it belongs to Kinoko Nasu and Type-Moon.

Cerberus

Part I

Cerberus blinked as one of her mental alarms went off, and turning away from watching young Issei Ryuudo struggle with his katas slipped further into the complex that was Ryuudo Temple. Here, at the intersection of three ley-lines, above the Holy Grail itself, Cerberus had made her lair. Spells allowed her to siphon off great amounts of prana from the ley-lines, as well as to pass herself off as a friend of the head monk who was currently boarding in the temple until certain circumstances had been resolved.

Slipping into one of several rooms she'd taken for herself, a gesture had several holographic screens come to life, and it was on one of them that Cerberus homed in on. Narrowing her eyes, she observed as a beautiful, platinum-blonde woman dressed in rich, silvery furs make her way through an airport terminal, chatting with her companion all the while. Said companion was…a woman? Possibly…she certainly had the face for it, though she – he (?) – could also just be a particularly feminine-looking man.

It didn't matter. The companion was dressed in a predominantly-black business ensemble, her golden blonde hair a good contrast with the other woman's platinum-blonde hair.

"Which do you think is the Servant, Assassin?" Cerberus asked.

Unnoticed, a pretty, adolescent-looking girl approached from one corner, Assassin having dispensed with her usual clothes and mask for something more modern, and to show her face to the world. Alone among those who bore the name of the Old Man of the Mountain, she had not sacrificed her physical identity as others had, if only to prevent one of her greatest, sharpest weapons as a bringer of death from being lost.

As is often said, a pretty face and a sweet voice are many a man's downfall.

"The one in black, I would say." Assassin answered after a moment. "The woman in white does not have the bearing of a fighter, and while she hides it well, the woman in black has what her Master does not."

"Hmm…and which Servant is she, I wonder?"

"Forgiveness…I have no answer."

Cerberus waved it off. "It's no concern right now." She said, before gesturing at the other screens.

Images shifted and displayed new – or old – information, updated regularly with information provided by familiars and spy mysteries. "All seven Masters have finally arrived." Cerberus said, indicating each screen in turn. "Tokiomi Tohsaka, Kayneth Archibald, Waver Velvet, Kirei Kotomine, that murderer down by the docks, myself, and this new arrival."

"Then it is only a matter of time before the war will begin in earnest." Assassin observed.

"Yes," Cerberus said with a nod. "Though something isn't right here."

"Master?"

Cerberus adjusted her screens, one of them displaying the Emiya mansion as viewed from three different directions. "Kiritsugu Emiya should be one of the Masters," she began. "And it does look like he's ready for quite a fight, given all the guns and explosives he keeps with him there. But…he has no Servant. Why?"

Assassin had no answer, and after a moment Cerberus turned towards her. "Infiltrate the Emiya mansion," she ordered. "Find out just what Emiya's game is."

Assassin bowed, and then vanished into astral form to perform her Master's bidding. Alone now, Cerberus turned back to her screens. She watched in silence for several long moments, and then shifted attention to another mansion in the suburbs.

"They're probably increasingly worried why they haven't received command spells yet." She thought. "Once the war begins in full, I doubt they won't be able to keep off on taking active action. Of course, all they'll be doing is walk into my trap of their own volition."

Cerberus smiled at the thought, though it was utterly without warmth.

In the darkness of Ryuudo Temple, a young woman worked in the light of the Moon to draw out a mandala on a wooden floor. Stones taken from the ruins of the fortress of Alamut had been ground into powder, and it was this powder that was used to mark the mandala.

Twin concentric circles with four smaller circles in the space in between in the four cardinal directions were drawn, followed by hermetic symbols in the smaller circles and along the edge of the inner circle. David's star followed, then another four smaller circles above the horizontal points of the star where they touched the outer circles. Hermetic symbols were also drawn within these circles, while at the heart of the star an esoteric sigil was drawn, unique to the mystery to be invoked, and completing the mandala's representation of what it was meant to achieve.

Moonlight glimmered on a drawn blade, and then on blood as the former was drawn across a palm. Blood dripped down in generous quantities on the mandala, which began to glow as a connection was forged and opened.

"Let silver and steel be the essence." The young woman began to speak the aria, the summoning ritual for her Servant in the Fourth Holy Grail War beginning in full. "Let stone and the Archduke of Contracts be the foundation. Let rise a wall against the wind that shall fall. Let the four cardinal gates close. Let the three-forked road from the crown reaching unto the Kingdom rotate."

Blood continued to drip down from the young woman's hand, falling onto the mandala's edge and causing its light to build as the ritual proceeded. With every spoken word the light pulsed, almost like a heartbeat, as the ritual built up to its conclusion, one way or another.

"Let it be declared now," the young woman continued. "Your flesh shall serve under me, and my fate shall be with your sword. Submit to the beckoning of the Holy Grail. Answer, if you would submit to this will and truth. An oath shall be sworn here: I shall attain all virtues of all of Heaven, and I shall have dominion over all evils of all of Hell."

The mandala flashed, and beginning to rotate, slowly projected a replica of itself rotating in sync above. "From the Seventh Heaven," the young woman concluded. "Attended to by three great words of power, come forth from the ring of restraint, Protector of the Holy Balance!"

The mandalas flashed to blinding, prana visibly swirling inside and coalescing into a lithe, toned, and dark-clothed figure that was all too feminine in its appearance. Short-cut hair shaded as though with amethyst waved in an ethereal breeze, the light of the mandalas glimmering on her silvered half-mask.

And then the light faded, Servant Assassin raising her face to face she who had summoned her.

"By your summons I have come." She said softly. "Answer me, are you my Master?"

"I am." The young woman answered.

"My arm is yours." Assassin said with a bow. "Might this one have the honor of your name?"

The young woman smiled. "I am Cerberus." She answered.

"Master,"

The thought came as Cerberus was taking her afternoon meal with the monks at Ryuudo Temple, simple but solid fare. White rice, miso soup with tofu and spring onions, steamed winter vegetables, and fried fish.

Cerberus put down her chopsticks, and lifted her soup bowl to her lips. "What is it?" she asked through her telepathic link.

"I have infiltrated the Emiya property as you ordered," Assassin reported. "And listening in on their conversation have uncovered the truth of his strategy. The new arrivals from earlier…the woman in white is Emiya's wife. And his decoy."

"Decoy?" Cerberus echoed before realization slammed home. "I see! Oh very clever…and ruthless too, to use his own wife to draw his enemies' attention, while he gets ready to shoot them in the back."

Silent laughter echoed through their telepathic linked, tinged with irony. "The war really changed you, Mister Emiya." Cerberus thought. "You're a very different man from what I remember of you. Anything more?"

"Yes, Master. I have uncovered the class of his Servant, if not her identity. She is the Servant Saber."

"Saber…shit, the most outstanding of all Servant classes. More importantly…hmm, a blonde swordswoman then, most likely. There's a lot of candidates for it, but given her North European features…Boudica, maybe? Joan of Arc? Who else could fit…regardless, we cannot afford to engage them directly. No offense intended, Assassin, but you are no match for her in a straight fight."

"I am aware, Master. And no offense was taken."

Cerberus put down her soup bowl and returned to her meal. "Withdraw for now, Assassin." She said. "There's no need for you to continue loitering there."

"Yes, Master." She said. "However, there is one other piece of information I have uncovered."

"Oh?"

"I have discovered Emiya's strategy to open the war with tonight." Assassin said. "He intends to have his wife and Saber go into the city, and observe them from the shadows. The latter will be disguised, at least physically, but will otherwise make no effort to conceal their presence."

"I see." Cerberus thought with narrowed eyes. "He's using her as bait. His own wife…Mister Emiya, just how ruthless were – are – you?"

"What should we do, Master?"

"I will consider our next move carefully. For now, withdraw."

"By your command."

As the link fell silent, Cerberus returned to her meal in silence, her mind already weighing the changes to her plans that Assassin's new information necessitated.

"You're going out yourself, Master?" Assassin asked with the faintest hint of worry.

"There's no rule that says Masters shouldn't stand on the front lines themselves." Cerberus said, while double-checking the seals on her armor. She wore a black bodysuit with a toughened exterior, while heavy trauma plates of super-strong steel alloy protected her limbs and torso, an armored waist harness, gauntlets, and boots doing likewise for her hands, waist, hips, crotch, and feet. "Conventional wisdom only dictates otherwise because Heaven's Feel is supposed to be a battle between Servants, and not Masters. But, conventional wisdom has never really applied to me. Not really."

Cerberus chuckled as memories floated through her mind, and finishing her checks, activated the mystic code built into her left gauntlet. It came to life with a whine, the large diamond fitted into the gauntlet's palm beginning to glow, and seeming to…suck in, the space around it. A moment later and the latter stopped, the mystic code entering standby mode until Cerberus had need of it.

"But," Assassin began. "With all due respect Master, you should not have to put yourself at risk. Such is my role as your Servant."

"That is true." Cerberus agreed. "But you cannot be everywhere at once. And Emiya requires…special, handling. No, you cannot play that role, Assassin. Not unless we want to kill him, and well, I don't want to. At least not yet. If necessary though…"

Cerberus trailed off, while looking silently into the distance, lost in her memories. Finally, she shook her head, and turned to look at Assassin.

"Follow the predetermined plan," she said to her Servant while strapping her sword, a wakizashi forged by Muramasa himself in the sixteenth century, to her left hip. "Follow Missus Emiya and Saber, reporting on the situation regularly."

"By your command."

Cerberus nodded, and lifting her helmet, fitted it over her head and sealing it with a hiss of pressurization. Then turning her head and regarding Assassin through a visor of specially-treated sapphire crystal, continued. "I will handle Emiya myself." She said, her voice muffled and changed by the helmet's speakers and scrubbers. "Now, let us go."

Assassin bowed and shifted into astral form, and a moment later Cerberus also vanished, in her case by absorbing any and all light falling onto her, and thus rendering her invisible to the naked eye. Slipping out of the temple complex and down the staircase, Cerberus reinforced her legs to move faster than she normally would be able to.

"Now then," Cerberus thought as she swept down the mountainside, towards the city of Fuyuki. "Let us turn to the matter of the war."

A/N

Once more with feeling, I guess.

As you might expect, 'Cerberus' is just an alias, and not her real name. And yes, it's as you read, she has past (?) history with Kiritsugu Emiya. Who is she then? A former lover? A relative? Someone he crossed paths/worked/fought with in the past? Who knows? We shall see soon enough. On a meta level, there is a video game reference between the alias and the description of her armor.

As for Assassin, it is rather obvious which incarnation of the Old Man of the Mountain she's supposed to be (for those not in the know, it's Hassan of Serenity).