(Before Caster's summoning)

If you were to look at Kariya Matou, the first question would be "What the hell happened to your face?!" Because there's no other way to describe the distorting horrors that his body suffered for a year due to the worms that squirmed through all his being, physically and spiritually.

And all that? All because a traditionalist and surprisingly neglectful (though not strange in magi society, figures) father gave his youngest daughter to a motherfucking, sadistic, heartless, bald, vampire of a worm without even asking what the goddamn 'training' that the poor girl was going to suffer through was about!

There was a reason Kariya hated his family and never came back to their house.

That was until he encountered his childhood crush, Aoi, who was now married to said asshole magus, Tokiomi Tohsaka, and told him that they gave Sakura to the Matou, his father, the cursed worm that talks, simply because mages cannot have more than one child?! Bullshit!

Tokiomi may see this as a blessing for his daughter, but nooo. Kariya knew better. And Sakura was paying dearly for it.

That was why he returned to his father; why he agreed to his hellish training and humiliation; and why he decided to fight in this war that will inevitably see him die, whether during or after it.

All because he wanted to save her and that's what he will goddamn do. Even if he goes to hell.

Right now, he was on the Matou basement, in front of a summoning circle excruciatingly drawn with his own blood after hours of spartan lessons trying to make a decent design, not helped by Zouken's cane (more like garrote) and the pain-inducing worms on his body.

To fight in the Holy Grail War, he needed a Servant, a copy of a famous Heroic Spirit that made its mark in history or myth and transcended to a level beyond humanity, wielding power that mortals could not hope to accomplish. As well as one of the main features of the Grail, for it is only possible for spirits to reach it and losing the Servant would be the same as losing the War.

Only one problem for Kariya… he was extremely weak as a magus. The majority of Masters were magecraft users with a lifetime of experience in their art so they would be boasting with technique as well as capacity for magic energy. A year of accelerated tutoring and crest worm therapy would not be enough to be at the same level as them. And again, Zouken didn't help much.

Fucking worm. He will cherish the day when that evil finally dies but sadly he won't be alive to presence it.

So, with few options available, Zouken proposed summoning a Berserker, Servants that traded sanity with overwhelming power that is on par or superior to the knight class Servants. Of course, with such madness, Berserkers are extremely difficult to control and will suck Masters dry of their prana whether trying to reign them in or just because of their augmented power expenditure.

And Kariya's crest worms apart from generating prana by devouring his body, also become… excited for lack of a better word when forced to generate prana, which does no wonders to his diminishing life expectancy of a month.

Once again, screw you Zouken.

Right now, he can only hope to summon a powerful Berserker that doesn't kill him immediately; have his revenge on Tokiomi; win the Grail and pray that Zouken kept his promise to free Sakura from the household and… and…

And probably have a family again, if not for him, then for Sakura.

Void Grail

The Keyblade Graveyard…

Once, the place where the Keyblade War provoked by the Foretellers and their Unions in a delusional belief of defending the Light from each other thanks to the manipulations of the Master of Masters, now only remembered as a conflict born from the lust of power Kingdom Hearts would offer and that shattered its counterpart, the X-blade, with its copies, the Keyblades.

This wasteland of broken weapons just recently suffered another Keyblade-related conflict, that while smaller, its consequences would and will be as great or more as the first War.

And one of the remnants of the last fight was here. A knight with earth colored armor and a greatsword-like Keyblade, remains prostrated, Keyblade point firmly fixed in the ground by his arms, silent in a timeless vow, maintained only with the remnants of memories and bonds past; the weight of his sins that he must redeem and an unquenchable rage towards the man who deceived him, killed his master; nearly turned his Heart against his friends and stole his body.

Yes, "he" was but a Lingering Will of a man who lost everything, except his weapon and will, to a madman. A ghost of a good man who fell into Darkness due to a will not of his own.

And who will wait, even for eternity, for that accursed man to appear, for it was in the Dark Seeker's fate to return to the Graveyard if he wished for the Keyblade War to reenact as well as Kingdom Hearts to awaken from its slumber.

Only then, will his vengeance be satisfied as well as his redemption be fulfilled.

For Aqua, Ven and Master Eraqus. His family. Terra's family.

Suddenly, the hollow armor felt something for the first time in what felt a long time ago.

[... A call?]

His disembodied mind then received information: Holy Grail War; copies of heroes past; seven pairs of Masters and Servants; a wish.

Normally, the Lingering Will would just ignore it. A battle tournament wouldn't helping in his future crusade against Xehanort, and while Terra would enjoy a good competition, in his current state it would be futile. And he wasn't desperate enough to abandon his vow for a wish that could allow him to finish Xehanort once and for all. He had too much personal stakes to allow something of dubious intent and existence to interfere with his revengeance.

However, he did also feel something else. The desperate and heartfelt wish of a dying man who's already sacrificing his own freedom and body so that a loved one would escape from a living nightmare.

Memories and thoughts of his failures once again tortured his metallic mind, especially of Ven's uncertain demise as well as Aqua's.

[No.]

As long as he's within reach, he won't let any evil to have its way to anyone else. That's what his friends would do, what Terra would do!

And by Kingdom Hearts, if the victim is a child he will destroy that Darkness so thoroughly that it will ever regret being born!

Besides, the Grail only requires a sample of his essence for the copy to participate in his place, his mission won't be interrupted by it.

Standing up, the Lingering Will took Ends of the Earth and pointed it to the sky, a Keyhole connected to the Grail appearing in the air.

Concentrating essence on the mystic weapon, he shot a beam of Light towards the Keyhole, accompanied with a locking sound.

Then he returned to his kneeling position. Waiting for Xehanort.

Though now he hopes that his other self will be enough to save those that needed help.

Void Grail

Zouken Matou was a man that lived for a long time, various centuries at least.

And that long life made him see failure after failure, especially after being forced out of his homeland Russia, which degraded the Matou, then Makiri, magecraft foundations as well as thinning their magi blood.

Not to talk about the soul degradation brought by trying to extend his life for centuries, ultimately devolving him into a cruel monster interested only in immortality, tragically forgotting why.

So it comes to no surprise that he'd like to win the Holy Grail War in order to be truly immortal. As well as wanting to see his prodigal son suffer from being much more of a coward than that spineless Byakuya.

Now? He has the opportunity to see his objectives accomplished!

Kariya dying? What a joy. Miraculously winning the War? Much better! Kariya winning the War then die? Hallelujah!

And best of all, it was thanks to that idiot of Tokiomi giving Sakura to him without much inquiry. Of course he would train her! If not as the Matou heir then as a vessel! And in the improbable but maybe not completely circumstance of Kariya returning to claim her after the War, he would of course kill him! After all, Zouken was still a magus and immortality or not, he would be an idiot to let go of such specimen with incredible magecraft talent.

So he let Bakariya take that hellish botched training and lend him the Matou basement to summon Berserker. At first, he thought in giving Kariya a catalyst, but his sadistic streak won out and decided to leave Kariya to luck.

Who knows? Maybe instead of a weakass Servant, he obtains a powerhouse that alongside high compatibility, will raise his chances in the War.

Oh, Zouken, maybe you should have thought better. For you are about to face the remnants of a Keyblade Master literally too angry to die that hates people like you.

Void Grail

The Lingering Will, no, Berserker, appeared on the summoning circle, in the same posture characteristic of his self in the Graveyard.

And he already wasn't liking what he was seeing.

There was a man in front of him that looked like he did barely survive a fire, what with the badly deformed face that looked half dead, more like he's dying. The man coughed up blood and was about to collapse.

Dematerializing Ends of the Earth, Berserker quickly and carefully caught the man in time. Now that he made contact, he can feel the prana from the ill man coming towards him from some marks in the man's hands, effectively making his Master.

However, he can feel the prana or magical energy being… twisted from lack of a better word. With a light taste of Darkness.

Examining his Master with Libra, he discovered that the man's body was infested with worms that alongside the already existing Magical Circuits, generated prana in exchange of life force, enormously crippling the body and possibly killing it.

By Kingdom Hearts… he knew that his Master was desperate but not THAT desperate.

Remembering some first aid lessons from Aqua and Eraqus, Berserker cast an Esuna, both as painkiller and a means to prevent the worms to be more excited than they already had, accompanied by a Cura to try to heal the most damaged body parts.

Terra may have been a hothead and less of a magical expert than Aqua but he wasn't dumb. Those worms may have been put there in order to accomodate for the magical cost that a Servant would impose to its Master, especially the ever magic-consuming Berserkers.

While the Keyblade Armor that conforms his body and his spellcasting abilities may reduce the strain, he was still far too powerful to go all out in a fight without worsening his Master's condition.

It was a complete lose-lose situation. Just what kind of being would subject a person to such a suicide action?!

"My, my, what an interesting Servant."

The armor shook his head towards the malicious voice. He only saw an old, decrepit thing with such a reek on Darkness that for a single moment, Xehanort's image imposed over it.

Without thinking twice, Berserker let out a furious metallic roar and with a free hand, unleashed a full powered Dark Firaga towards the evil entity. The Darkness-imbued fire spell exploded on the target, making it and the worms that plaged the house to scream in agony.

Fortunately, Berserker's Master was already protected by his Servant placing himself as a barrier. Also, the Dark Firaga was powered by Berserker's rage so not a drop of prana was drained from the poor Master.

Unfortunately, the thing wasn't dead yet.

"Tsk! What a problematic Servant…" The same condescending and malicious voice reverberated through the worms placed in the walls with barely restrained fury. "Kariya! Go out of my house until you win the Grail! I cannot have this Berserker ruining all my life's work just because you fail to control its anger!"

Berserker's fury grew. He never thought he would ever find someone as rotten as Master Xehanort, guess he was wrong.

Just as the Servant of Madness was going to rip apart the house, a Command Spell beginning to activate made him pause.

Turning towards his Master, he instantly knew. Both on his good eye and their bond, the Master expressed the same anger as Berserker, enough that he would let the Servant do as he wished but couldn't for some reason or another.

Understanding, Berserker gently helped his Master to stand up. The Master was surprised though, whether for the apparent self-control of Berserker or the fact he could feel again part of the left half of his body or both.

"Thanks." The Master croaked out "Let's go." And both went towards the stairs, no one wanting to be on that accursed place for long.

Void Grail

"Uncle Kariya?" What Berserker didn't expect was for a child to be in this hellhole. This wasn't a place for a little girl. And he was correct.

The girl's gaze looked even more dead than his Master's, not helping was that he could feel the worms in her body as well as the Darkness in her Heart.

That… was worse than he imagined, no children should be like this. No one should suffer the same horrors that girl experienced to the point of breaking her Heart, ending up as a hollow shell.

"Sakura?" Kariya, the Master, lit up in recognition "What are you doing here? Shouldn't you be in your room?"

"I… am scared." Sakura hugged one of Kariya's legs "Grandfather… he's angry. I can feel it in the worms."

Even when Berserker's limited emotion range consisted mostly of anger, he couldn't help but feel a semblance of guilt.

That evil thing, Zouken, must be connected to all the worms in the house, including Kariya and Sakura's, so when he burned that thing's body, not only did it survive, he put the child, and possibly his Master, at risk because of his anger. What would his friends and family think of him now?

"Don't worry, Sakura." With a warm smile, Kariya caressed her head "I promise that we will leave this house together and never come back."

"You promise?"

"Of course."

"And will I be able to see Rin, Mom, and Dad?"

Kariya turned a little uncomfortable at the last word but didn't show it externally. "Of course, we will be a family again."

That sparked a Light in Sakura's Heart that Berserker thought completely extinguished. No, it was always there. It has been present, allowing Sakura to go through all those nightmarish trials without completely losing herself to that insurmountable tide of Darkness. That Light… represents her Hope in one day escaping that mansion and regain her life.

Berserker was left astonished, if possible, at that strenght of Heart, more powerful than any Keyblade Wielder he met, what with most of them succumbing to Darkness, directly or undirectly, including him.

An idea formed in his hollow mind. It may not work due to already doing it once, but that was with his original body. But he was now a Servant, a copy of the remnants of a Keyblade Wielder, so maybe…

Berserker kneeled in front of Sakura, who shyly took refuge in Kariya's leg. The man was about to question his Servant's behavior when he blinked at sensing Berserker's urge for permission. Kariya took a look at Sakura, then at Berserker. He didn't know what was happening but after seeing Berserker healing him as well as calming down on his own, he decided to take a leap of faith.

After reassuring to Sakura that Berserker was safe, the insecure little girl decided to trust her uncle and exit her refuge.

[Hello little one.] Berserker presented himself with a monotone metallic voice that was oddly warm. Years of raising Ventus gave him plenty of experience with children.

"He-hello." Sakura shyly said "Who are you? A knight?"

[Of course I am a knight, little one.] Berserker let out a chuckle, then summoned Ends of the Earth in a reverse grip and offered it to her.

["In your hand, take this key. So long as you have the makings, then through this simple act of taking, its wielder you shall one day be. And you will find me, friend. As long as you maintain hope, your Light will never go extinct. And from this nightmare, you will wake."] Berserker recited the ritual words of the Bequeathing, the ancient ceremony that allows a Keyblade Master to choose an inheritor of the Keyblade. Terra already did it to that kid in the islands but with Berserker being technically a different person, it may be successful in this try.

Slowly, Sakura's hand reached towards the Keyblade hilt.

And took it.

Void Grail

"What was that?" Kariya asked Berserker once they were out of the Matou manor, for once having less dificulty to do so after his training.

[A… countermeasure of sorts.] The astralised Berserker replied through telepathy [There's no guarantee that we will survive the War, so I gifted her with a power that will help her through her time within that house.]

"I guess I should thank you again, then." For all magecraft did for his life, Kariya felt grateful for something that came from it. "But I guess it will be for null once we win the Grail."

[I wouldn't be sure of that, Master] Berserker replied [You're dying, and while I know powerful healing spells, I won't be able to recover all the life force you've lost. And a more permanent soultion would require to extract all the worms, which would severily affect my fighting performance. Besides…] Berserker's voice gained a subtle angry tone [I knew once someone like that Zouken. Never trust him. It would take you turning your back on him to stab you and completely take control over Sakura, promises be damned.]

Kariya let out a curse. While he knew Zouken wouldn't have an immediate use for Sakura were he to gain the Grail, Zouken was still a magus. And magi society is full of amoral manipulators and traitors that wouldn't doubt on turning against their families and friends if they think it would be helping their research.

He was so desperate and unfeeling by the pain that he forgot about it.

"Then… what should we do." Kariya let out, right hand bleeding by the nails pressing in the skin.

[For now, we focus on the War. And when we see an opportunity, we'll take it.]

For Berserker was not stranger to vengeance, and was patient about it. But when you're the object of his fury, pray.

AN: Rage Awakens intensifies. Finally! I've finished Fate/Zero anime, now I need to continue with the novels!

What? Thinking I wouldn't continue with one of my fics. Well you were wrong. I finally have summer vacation! That also means I have games, series, fics and manga I want to finish so no complete guarantee. I'm also reading Fate: Desiderantes Afectibus by the time of writing this chapter. I reccomend it not to tell that it inspired me a bit.

So anyways, I decided to put Lingering Will as Berserker, well, I initially thought on maintaining Lancelot but I already had other Fate/Zero fanfics planned so I decided to make this Berserker different from normal as well as being pretty fitting knowing who's also there.

It wasn't till in the middle of it that I remembered another Fate crossover with Lingering Will on it, Sword of Earth, where LW found Shirou during the Fuyuki Fire and decided to offer its body (armor), mind and Keyblade to help save his life. Sadly, it was discontinued at the beginning of the Fifth Grail War arc.

Well, here is Berserker's Servant sheet:

Berserker-Lingering Will

Strength: A

Endurance: A+

Agility: B

Mana: A

Luck: C

NP: A

Skills:

Mad Enhancement (EX): A unique case of Mad Enhancement were instead of driving the Servant mad, madness is the main impulse of Lingering Will. In other words, he's not so different from wraiths with unfinished businesses in this world, in this case, vengeance. Berserker doesn't gain any stat bonuses (not that he needs them) and is able to act rationally. However, present him anything related to Xehanort and will definately go batshit crazy to kill it. Misunderstandings or not. He can also enter a proper Berserk state as a desperation attack.

Mark of Mastery (False) (B): While not a Keyblade Master, Terra trained extensively to become one, with his travels only serving to further refine his skills. Because of that, he's able to perform Master-level techniques like the Bequeathing. That skill also gives him Eternal Arms Mastership (A+), Formchange (A), Magecraft (B).

Eternal Arms Mastership (A+): Even when full of fury, Berserker maintains all of his battle mastery. Which combined with the powers of a Keyblade, it transforms its user into a veritable one man army. It complements Formchange and Magecraft.

Formchange (A): An advanced Keyblade technique, Berserker mastered its use to levels even Keyblade Masters think as excessive. Apart from a hoverbike-like Glider, Berserker is able to transform his Keyblade into a myriad weapons: drills, whips and the powerful Ultima Cannon.

Magecraft (B): While being a physical oriented fighter, all if not most Keyblade Wielders are experts in the use of combat magic as well as swordmanship. Berserker is able to execute most Black Magic (Fire, Blizzard, Thunder...) and some White Magic (Cure, Esuna...), though Berserker decants more towards Earth and Darkness elemental spells, though he can inflict seals that disable the victim's attacks and magic. He can also summon bits or drones with the ability to fire beams towards the enemy.

Battle Continuation (A): Just ask Sora and Xehanort why that armor never seems to die.

Noble Phantasms:

Keyblade: Ends of the Earth (Anti-unit; A+): A conceptual weapon made from one's heart, each Keyblade is a copy of the original x-blade that guarded Kingdom Hearts, an equivalent of Akasha in the infinite omniverse. The high rank comes from the Mystery that surrounds the Heart and the infinite possibilities (Light, Darkness) it possesses. If it were the original x-blade, it would be ranked EX. While this Keyblade isn't one of the most powerful ones, its a surprisingly well balanced weapon, giving great physical strenght as well as decent magic might. The Keyblade is able to lock and unlock any lock, physical and metaphysical, including even the Hearts of Worlds. The Keyblade is also a natural conduit of magic making it an ideal foci for spells and despite most of them lacking a cutting edge, they can be impossibly sharp. A Keyblade, a somewhat sentient weapon, chooses its own owner, making it nearly impossible to steal unless the usurper has an exceptionally strong Heart or are already Keyblade Wielders themselves. There are even more functions unknown about it that the user may discover, whether by luck, practise or pure determination.

Keyblade Armor: A Mind's Vessel (A): A traditional piece of equipment for Keyblade Wielders of old, it's also very practical due to protecting its user from interdimensional and/or mystical interference as well as harsh environments like the Darkness between Worlds or the cold void of outer space. It also protects the wielder against the supernatural-surpressing effects of Gaia's Reality Marble, allowing for greater efficiency in magic energy management as well as being a blind spot for the Counter Force. Usually, the Keyblade Armor should only rank as a E or D Noble Phantasm or Mystic Code but due to it being practically Berserker's body it has a very high rank. However, that also makes him vulnerable to some Noble Phantasms like Gae Dearg, that while not killing him instantly, can immobilize him enough to receive a definitive kill attack so take caution. Theoretically, given its autoadjusting and materializing properties, it should be possible for anyone to wear that armor to receive its benefits, including Berserker's huge power and weapon, without side effects. However, Berserker is the one ultimately controlling the armor's movements so it should be preferable to maintain a healthy relationship with him unless you want him to imprison you in the armor due to being evil or a dick.

I fused his status as a superboss and a KH protagonist, so I bet all Masters and a few Servants will have a bad time, especially Gilgamesh and Vanitas.