Fanfic / Fate/Joyous Order

Fate/Joyous Order: Mash and Charlie's Awesome Adventure is a Fate/Grand Order and Fate/Extella Link crossover by auraofcalm where a reincarnated Charlie becomes the Master of Chaldea.

Following the events of Fate/Extella Link, Charlemagne was reincarnated as a human in the Grand Order timeline via Moon Cell shenanigans. Almost two decades later he decides to join an organization named Chaldea on a 'hunch', and when things predictably go awry he resolves to live up to his legend by smiting evil-doers and being as awesome as humanly possible.

Fate/Joyous Order contains the following tropes

• Achievements in Ignorance: After reading the rulebook post-Fuyuki, Charlie rationalizes he at least deserves a title (and a nameplate) for being one of the few people on active duty and decides to fill out his forms for Field Commander. He gets all that, along with outranking other people like Dr. Roman, who is then seen in pure disbelief that Charlie unintentionally performed a bureaucratic coup.
• Adaptational Badass: By virtue of having a different protagonist. Instead of having a third-rate Magus who's had no involvement to anything supernatural related prior to Chaldea, it's the reborn King of the Franks himself who's gone through the events of Fate/Extella Link that's taking the reins.
• Adaptational Personality Change: Downplayed. Mash is still the Shrinking Violet Nice Girl everyone's familiar with, however having Charlemagne as a Master causes her to show a degree of exasperation at his antics, doing a Facepalm at certain occasions and even slapping him out of reflex once when Charlie showed Charles Patricius for the first time in the Orleans Singularity, something she really wouldn't even do with Ritsuka. Though, it's mostly Played for Laughs as she nonetheless calls him "Senpai" and treats him with respect, as well as having shades of being a Clingy Jealous Girl when she thought that Charlie prefers girls like Olga, not to mention being taken aback when Kiyohime basically invaded his personal space.
• Adapted Out: Ritsuka Fujimaru is not present in the story, with the reincarnated Charlemagne taking their place.
• Belligerent Sexual Tension: Between Charlie and Olga.
• Big Damn Heroes: Who should help Charlie against the possessed Lev but Archer EMIYA.
• Brought Down to Badass: Since Charlemagne is a Servant reincarnated into a human, he can't fight like how he was in the Moon Cell, especially since he has to devote some energy into the Servants he summons. That being said, he can turn back into his Servant form when needed and retains all his skills and abilities, although this tires him out. Even as a human he's better off than Ritsuka, having more magical circuits and all of them in decent quality.
• Bunny-Ears Lawyer: Charlemagne acts like a guy on a sugar high, being easily excited about a lot of things and trying his best to always look cool. That being said, he is Charlemagne, The King of the Franks, leader of the Twelve Paladins and Father of Europe, so calling him incompetent isn't exactly accurate.
• Contrived Coincidence: Lev takes a moment to complain about all the setbacks and surprises he's been dealing with; from Olga manifesting as a ghost, Mash awakening her power, to Charlie showing up and being King Charlemagne reborn. Charlie's agreement makes him wonder if it's Alaya going against him.
  Charlie: “Yeah. It’s almost like the World itself was out to get you.”
  Lev: "You believe yourself, or at least your presence here and now, to be a manifestation of the Counter Force?"
• Cutting Off the Branches: Charlie mentions his master, Hakuno Kishinami, being male. While this was already canon with story materials provided in Fate/Extella, there is the option to play the game as female Hakuno instead, even though they're treated with male pronouns.
• Death by Adaptation: Lev Lainur perishes at the end of Fuyuki, thanks to Joyouse Ordre and a clutch save from Emiya.
• Denser and Wackier: This is kind of inevitable considering we have a reincarnated Charlemagne, instead of an Action Survivor Master who got thrown into the wolves. The first prologue Singularity they end up in, while not devoid of serious moments, involves a few funny moments, especially with The first Servant he summons is Astolfo, and considering how the Paladins of Charlemagne are.... Though time will tell just how long this levity lasts.
• Fun Size: Olga in her new body provided by Da Vinci. She's not pleased at all.
• Good Parents: Jeanne's parents, Jacques and Isabelle, are very accepting of her condition (being a revived Heroic Spirit) and defends her honor when they think Charlie is accusing Jeanne's of being the Dragon Witch.
• Jerkass Has a Point: When Charlies asks Olga about the Demi-Servant experiments that Chaldea have been conducting, she states that he has no right to judge it, considering that he massacred the Saxons for not converting to Christianity. And unlike him, she has nothing to do with the experiments. This caused Charlie's face to become red in anger.
• Know When to Fold Them: The corrupted Emiya in Fuyuki only fought Chaldea because he served Saber Alter; with her defeat, he has no reason to fight anymore, and even helps Chaldea defeat Lev and save Olga.
• Nice Job Breaking It, Hero: While Charlie and his team fight Vlad and Carmilla, Marie Antoinette arrives to help... except for the fact that she decides to help d'Eon against Kojirou on the assumption that her loyal retainer was also on the side of humanity. Whoops.
• Oh, Crap!: Olga's reaction upon realizing that she "kicked the Father of Europe in the ass" after Charlie revealed his identity.
• Power-Strain Blackout: Charlie using his Servant form will leave his human form in a much weakened state. Astolfo even notes he can barely stand once they return from Fuyuki.
• Reasonable Authority Figure: Charlie after being promoted to Field Commander. He only applied just so he would have a title, but when he gets that title he actually starts doing his part to raise morale and better organize Chaldea's remaining staff, and approves of Romani and Da Vinci's requests immediately to stay out of their way. Romani even expresses surprise that he's actually doing the job, to which Charlie admits he wanted to help out in a way other than swinging a sword around. Once Olga's new body is ready, he immediately relinquishes authority back to her.
• Soul Jar: Olga's soul is stored in the Fuyuki Grail in order to save her life. Da Vinci later decides to keep the soul in the Grail and having Olga "remote pilot" her new body, figuring that it would be safer there.
• Spared by the Adaptation: Olga dies at the end of the Fuyuki Singularity in canon, but here she gets saved using a ritual that put her soul into the Singularity's grail and Da Vinci later hooks it up to her backup body.
• Sure, Let's Go with That: When Charlie is excited on reuniting with Robin, because the latter is not the same one, he pretends that he knows Charlie and is happy to meet him again.
• What Could Possibly Go Wrong?: In Fuyuki, Charlie states that the speed of Hippogriff means that Astolfo doesn't need to be afraid of arrows even if they are shot by a Servant... except that the Archer is EMIYA.