Fate Stay Night: Ultimate Master is a Cross OverFanfic between Fate/stay night and Ben 10: Ultimate Alien written by Ten-Faced Paladin.The fic is chronologically set after the event of season 1 from the Ultimate Alien perspective, but in an Alternate Timeline of the Fifth Holy Grail War from the Fate Stay Night perspective. It starts with Ben Tennyson being sent in Japan by the Plumbers to investigate on the murders and "Gas leaks" that took place during the Great Fuyuki Fire. As he is visiting Fuyuki City, he ends up attacked by Lancer, then looking for souls to feed on. However, as a result of both a latent source of Mana he got from his Adonyte blood and a mysterious manipulation of the rules by an unknown source, Ben ends up being selected as a Eighth Master, with a female Avenger (strongly hinted to be Joan of Arc) as his Servant. Though initially disturbed, he decides to stay in order to ensure the Grail won't fail in wrong hands.The fic can be found here. Five chapters have been published so far, with the fifth being released on October 11, 2013 after a long hiatus.
This fanfic provides examples of:
Accidental Pervert: In one scene, Shirou is trying to heal a partially naked Saber from the wound she got following her battle with Avenger. Rin shows up precisely as this point. Guess how she interprets the scene before learning about the wound.
Adaptational Badass: Avenger, both as a class and as a character; As a class, the Hollow Ataraxia Avenger was the weakest of the Servants, while this one can go toe to toe with Saber in a fight. As a character, the Joan of Arc from Fate/Apocrypha can't use her Noble Phantasm without killing herself, while this one can.
Adaptational Villainy: A minor example with Caster's original Master. In the source material, few details are given about him, but the reason Caster killed him for the first place apparently was due to him disrespecting her and constantly trying to humiliate her. In this version, he apparently tried to use his Command Spells to rape her. This could be a case of Unreliable Narrator, seeing how Caster is the one narrating the tale, but the canon established that Heroic Spirits cannot lie, so there has to be some truth in it.
Alien Blood: Since the Nasuverse is generally Bloodier and Gorier than the Ben 10 Universe, the author allows Ben's aliens to get actually visible damage, leading to this.
Alternate Continuity: Apparently, this continuity has the Ben 10 universe and the Nasuverse merged as one universe, with interactions mentioned (Shirou saw pics of Ben's aliens at school, Ilya is a Ben 10 fangirl, Kotomine mentions the Church has been considering recruiting Ben, before deciding he wasn't easy to control, Rin mentions the Mage's Association has been chasing Hex and Charmcaster for their crimes, and in the past, Saber met the Forever Knights who attempted to steal her sword). For the Route aspect, it includes elements from all three routes, plus some from Hollow Ataraxia (use of the Avenger class and Bazett being restored to life).
Lampshaded by Archer, who fears he is in an alternate timeline since he doesn't remember anything like Ben.
Attempted Rape: According to Caster, her original Master tried to use his Command Spell to rape her. Anyone familiar with the series knows how that ended.
Awesome by Analysis: After only two fights against Ben, Archer is able to find out his weakness, and even actually succeeds in hurting him. In Humongousaur form.
Back from the Dead: Paradox restores Bazett to life with her Command Spells back so she can free Lancer from Kotomine's control.
Batman Gambit: Aware that she doesn't stand a chance against a potential alliance of Ben and Ilya in a direct fight, Caster relies on this to face them. She attacks them with her skeleton familiars, willingly attracts Shirou and Rin there, then retreats to leave them fight each other in the hope at least some of them will get killed.
Her attempt to negotiate with him might be another one.
Battle Couple: Ben and Avenger, though not romantically involved (yet), fit this trope in every other aspect; both are competent in a fight on their own, and each of them is willing to do everything to protect the other. This actually gets complicated when Avenger gets puzzled about her Master insisting to fight by her side and tries her best to convince him to let her do her job.
Obviously, Shirou and Saber.
Caster and Kuzuki too, though Caster tries to hide it so Ben will think her Master is defenseless and help her.
Beam-O-War: subverted; Avenger and Saber try to use their respective Noble Phantasms against each other, but Gilgamesh stops them by unleashing Ea, leaving both of them injured.
Berserk Button: Saber doesn't take well to being mistaken for Morganna, and even less for a thief who stole Excalibur.
As usual, putting civilians in danger in front of Benalways is a bad idea.
Bifauxnen: Avenger in her civilian attire. Ben's reaction says it all.
Big Bad Ensemble: In addition to Kotomine and Gilgamesh, Matou Zouken was able to hoodwink the rule of the Holy Grail War to summon True Assassin of his own, meaning the Big Bads of both routes are active.
Blood Knight: While Lancer is shocked to see Avenger being summoned and Ben transforming, it also gets him more excited about the fight that will result. He is actually mad when the Command Spell forces him to retreat.
Lancer: "Not quite what I was expecting tonight, but I sure as hell ain't complaining!"
Also, Gilgamesh seems quite interested to learn that a new Avenger with a super-powered Master has joined this war:
Gilgamesh: "Hmm, and here I thought the only interesting points of this War would be the demi-god and Saber..."
Bodyguarding a Badass: This essentially sums up Avenger's position toward Ben. Avenger is powerful of her own, but Ben definitely is capable of defending himself of his own, and the versatility of his power makes him much more of a treath than her. Played with in later chapters, where some characters actually manage to hurt him and he is forced to call for her help. Eventually, she becomes Genre Savvy enough to adapt and convince him to train into coordinating themselves in fights.
Boring Invincible Hero: Subverted; Ben technically overpowers pretty much everyone in the War other than possibly Gilgamesh, and everyone is aware of this, resulting in him being seen as the biggest threat. However, this is balanced by both his usual Ultimatrix glitches and his reluctance to kill both civilians and other Masters, while his opponents make up for it by acting much more pragmatic and smarter.
Combat Pragmatism: both Archer and True Assassin use this against Ben. Notably, they are those who come the closest to killing him because of it so far.
Avenger suggests this strategy to Ben by saying they should identify and kill the Masters as a priority, but he violently rejects the idea, even threatening her to use a Command Spell.
Continuity Nod/Call Back: A lot to both series involved. Seeing how the story mainly focused on Fate/Stay Night, which always develops the characters' past a lot, that's not exactly surprising.
At the beginning of the first chapter, Ben, while arriving to the city, read his report on the event at Fuyuki City, including a list of all Masters in Fate/Zero and the various way their bodies were found (or, in Waver's case, not found.)
Lancer also mentions fighting Saber a few minutes before Ben, much like in the actual game;
While Ben (and later Paradox) are the only characters from Ben 10 to actually show up, Ben has many flashbacks about both his adventures and his friends; he mentions feeling guilt for almost killing Kevin, and tends to imagine what Gwen and Kevin would say when Avenger tries to sleep in the same bed than him. His guilt about Kevin, particularly, serves as his main reason to not kill the Masters.
When Caster describes the Root of Existence to Ben, this causes him to remember the Forge of Creation.
Her research on Ben also ends up showing a lot of references to previous episodes, including Way Big fighting a Black and Blue version of himself in Japan (a nod to the video game Ben 10 Cosmic Destruction) and Will Harrangue's campaign.
Cool Shades: Avenger wears these in her civilian attire.
Cool vs. Awesome: Pretty much any fight involving one of Ben's alien forms against a Servant.
The Dreaded: A rather toned down and comedic example, but Ben tends to raise concern amongst everybody else; his involvement in the war was unexpected by everybody, he has a decently powerful Servant of his own, and he is himself overpowered thanks to the Ultimatrix. The only one who doesn't seem concerned with him is Gilgamesh, for obvious reasons.
Emerald Power: Guess which color Ben's mana glows when Avenger is summoned. Go on, guess.
Enemy Mine: Ben does team up with various other Masters and Servants on several occasions:
He is offered an alliance by Ilya, and both fight Caster side-by-side. He however turns briefly against her when she attempts to kill Shirou; though the alliance isn't exactly broken, she forbids him to hang around with her for three days as a punishment.
Caster attempts to negotiate with him after this; he ends up helping her by protecting her temple while she took her Master to safety. It's strongly hinted this was part of a plan she has to manipulate him.
Paradox mentioned that he and Shirou would team up at some point, which would lead to a major turn in the events. Chapter 4's end suggests it's about to happen.
Avenger's identity. The author hasn't revealed it in the story yet, but there are more than enough clues to say for sure she is Joan of Arc.
In-universe, Ben's fame. Since he isn't quite as known in Japan as he is in America, he tries his best to keep a low profile, even refusing to give too much detail about himself to his own Servant. However, Kotomine heard of him from The Church, the Einzberns had been following him for a while, and Rin ends up finding information about him on the Internet.
Expy: Avenger is one of Saber, sharing both a similar look, fighting style and part of her personality. Justified, since her true identity is Joan of Arc, who is indeed an Identical Stranger to Saber in the actual support. Plus, Ben being similar to Shirou in many ways, her acting with him like Saber does toward Shirou is logical.
Fangirl: Ilya turns out to be this to Ben; she takes as much pleasure in fighting him as in seeing him transform during their fight.
Fanservice: Avenger in pyjamas after taking a bath.
French Jerk: Averted; Avenger is french, but a pretty nice person.
Gas Leak Coverup: Used as a plot point; the Plumbers aren't that easily fooled by the excuse and decide to secretly investigate about it. This is what led to Ben's trip to Japan.
Getting Crap Past the Radar: The fanfic avoids directly involving sex scenes like one of its original materials, but there are still elements included:
Good Is Not Dumb: While he can act a bit naive compared to other Masters on occasion, Ben mostly is portrayed in this fic as very Genre Savvy and fairly intelligent when the situation calls for it (in contrast to his later portrayal). He keeps an eye on the Servants' stats regularly, usually picks the right form for each situation, suspects the Holy Grail might be a Jerkass Genie and generally knows how to take advantage on his experience.
Good Vs Good: Ben and Avenger clashes several times with either Rin and Archer, Shirou and Saber, or both at the same time. According to Paradox though, Shirou and Ben will team up eventually.
Green-Eyed Monster: Shinji; while this isn't exactly new compared to the original material, the parts following his perspective put a lot of emphasis on his devouring jealousy for both Sakura, Shirou, and later Ben, because all of them can do things he isn't capable of.
Guile Hero: Paradox seems to be having that position in the Holy Grail War.
Half-Human Hybrid: while he still lacks actual Anodyte powers, it's revealed that being 1/4 Anodyte still gave Ben a natural source of Mana, allowing him to provide Avenger with an acceptable amount of it.
The Juggernaut: Berserker, when confronted by Ben; he brushes off Cannonbolt's charge like it's nothing, is barely injured by Ultimate Cannonbolt's charge, and still keeps advancing even when tortured by Echo Echo's sonic scream.
Know When to Fold 'Em: Lancer is, like in the original material, forced to follow this Trope by his Master's Command Spell, much to his dismay.
Used and reused by Caster as part of her schemes.
Shinji instructs Rider to attack Caster's temple with a particularly bad strategy. Though she is unable to disobey him, Rider is fully aware of how doomed this plan is, so she decides to only attempt one attack and then use Loophole Abuse to leave. It does get a bit more complicated than that, but she succeeds eventually.
True Assassin eventually is smart enough to accept that his attempt to kill Ben has failed and to leave for now.
Mr. Exposition: Avenger and Kotomine successively explain Ben to the way the Holy Grail works.
Mugging the Monster: At the beginning of the fic, Lancer tries to attack Ben in order to feed on his soul. He is extremely puzzled to see what he believed to be a harmless human teenager turn into an armored alien with fire abilities.
Noodle Incident: Paradox met Cu Chulainn when he was alive, and apparently got along well with him.
Not So Different: Ben and Shirou are much alike in many ways; both are in the war solely to ensure the Grail doesn't fall into the wrong hands, both have a huge Chronic Hero Syndrome, and even their Servants are a lot similar both physically and mentally. Rin actually lampshades it.
The similarities become even more blatant when the two actually get to talk together:
Ben (sight): "Magic. I was never good at dealing with magic"
Again in chapter 5, when Rin finds him bearing an unconcious Saber in his arms.
Ben is terrified of ending up in such a situation, should Gwen see him sleeping in the same bed than Avenger.
Oh Crap: Lancer's reaction to Avenger being summoned as Ben's Servant.
Lancer: "Oh no! OH HELL NO! IT'S IMPOSSIBLE! THE SEVEN HAVE ALREADY BEEN SUMMONED!"
Ben has a big one when finding out Berserker can handle an Ultimate Cannonbolt charge like nothing. Even more so when he actually reads his profile and finds out about his Noble Phantasm.
Caster has one when she sees Ilya offering an alliance to Ben.
Used as a Running Gag with Rin each time she gets to see another one of Ben's alien forms.
Nearly every Master and Servant has this after seeing Ben turn into Way Big. This is in fact what causes Matou to send True Assassin after Ben.
Overshadowed by Awesome: In-Universe example; Avenger clearly is a powerful Servant, able to stand of her own against Saber, but her Master's unusual ability to shapeshift tend to cause everybody to be more concerned about Ben than her. Lampshaded by Archer.
Playing the Victim Card: After finding out about Ben's Chronic Hero Syndrome, Caster decides to confront him in person, rather than fight him again, and tell him partially about her origin, hoping he will take pity on her and agree to either an alliance or a truce. It's however later suggested that it's only part of another one of her plans.
Samus Is a Girl: Played with; Avenger wears a helmet when fighting that covers her face; however she is bare-headed when first introduced, so the trope technically is averted from Ben's perspective; from Shirou's, Shinji's, and Saber's, on the other hand, it seems to have been played straight.
Ship Tease: Much like Saber, Avenger insists on sleeping in the same room, and even in the same bed, as Ben. The difference is, much to Ben's embarrassment, she succeeds. If the narration describing his impressions is anything to go by, he isn't indifferent to her charms.
Saber and Shirou also get some of this, most notably in the scene where Shirou heals her wounds. YMMV if Rin's reaction to said scene counts as it.
Show Their Work: Ben's dream of Avenger's past includes mention of actual historical places in France that were important in Joan of Arc's backstory.
The Starscream: Shinji's perspective makes it clear he intends to betray his grandfather and get the Grail for himself.
The Stations of the Canon: Played with. All three routes plus a bit of Hollow Ataraxia have been mixed; as a result, some scenes and events from the canon do happen, though most of them offscreen (since the story mostly follows Ben's perspective), and some of the scenes are changed; for example, the confrontation between Saber and Rider is interrupted by Ben and Avenger, and Zouken is able to summon True Assassin without being required to kill Sasaki Koujirou due to the twisting of the rules. The fight between Saber and Assassin from Fate, on the other hand, does happen and is identical to the original version, but has more important consequences (such as leading to an interaction between Ben and Shirou).
Thou Shalt Not Kill: Ben is still recovering from his guilt about almost killing Kevin at the end of season 1, and as a result is extremely reluctant to rely on lethal methods, even in the Holy Grail War. He does compromise with the Servants, considering that since they are doomed to disappear anyway and are aware of the consequences, but he still refuses to kill the Masters. Of course, everyone around him other than Shirou find this reasoning foolish and naïve.
Considering that if your name isn't Ben or Shirou, as a Master you entered the Grail War knowing exactly what that entailed (or at least as much as any of the Servants do), it's not surprising that they don't consider themselves bystanders.
Transformation Name Announcement: Since this is the Ultimate Alien Ben, he retains the habit of calling out his aliens' names. This is actually used against him when Rin is able to find information about him by searching the aliens' names on the internet.
Underestimating Badassery: This is apparently the reason True Assassin failed to kill Ben; he underestimated Armodrillo's reflexes and Ben's ability to shapeshift and adapt to the situation. Notably, all characters are clear on the fact Ben got lucky and this won't happen a second time.
Weak, but Skilled: Archer possesses, as usual, one of the weakest profiles amongst the Servants. Yet he is the first guy to actually succeed in hurting Ben for real.
Also, Rider, who successfully stood her ground against the combined forces of Ben and Avenger during their fight in the Ryuudou temple. This despite the fact that she is using Shinji as her Master, Avenger is as strong as Saber and Ben is in Armordrillo form.
Wild Card: Ben is seen as this by everyone else in the Holy Grail War; his only interest is in preventing casualties or lost of innocent lives, including the other Masters. As such, he will team up with anybody just to protect other Masters, but will just as easily turn against them if they cross that line.
Worthy Opponent: Played with between Saber and Avenger; they seem to genuinely respect each others' fighting prowess, but their fight tend to also include insults and arguments.
Why Won't You Die?: True Assassin gets extremely frustrated by Ben's resilience to his murder attempt:
To an extent, Ultimate Cannonbolt too; despite being one of the strongest aliens, he barely succeeds in hurting Berserker, and the little damage he does cause is instantly healed, much to Ben's dismay.
You Called Me X, It Must Be Serious: Due to Ben's insistence, Avenger usually refers to him by his first name. She however revert back to calling him "Master" whenever she is trying to have a serious talk with him or if the situation is particularly serious.