Pre-notes: Just to makes things clear, This story occurs post-Doom eternal. The only difference is that the Slayer was able to get Vega back from Urdak in this story.

Enjoy!

Chaldea

The Slayer walks about the white corridors of the headquarters of the Chaldea Security Organization. It was a rough ride from the collapsing singularity of Fuyuki, but all four of them made it out alright. A medical team had to get the three youngsters to medical as they were found unconscious upon returning, leaving the Slayer to walk about and explore. The place looked fancy with it's white, pearly colours contrasted with the dark blue of the main core room. It was different from the UAC facilities he's used to; however, there was no blood or corpses laid about so that was a major positive for the place. As he continued to explore he found some windows that revealed the outside environment that surrounded the base. It was a frozen landscape for miles, no signs of life over the horizon, nor clear sky to give him an idea where this place was on the planet. If he had to guess from experience, he had to be somewhere in either one of the polar locations of earth or maybe Canada?

He let out a small chuckle at the thought, something he rarely ever did as a Demon-Slayer. Vega could probably tell where they were but the AI is currently occupied dealing with helping the remaining staff repair the place in many sections of the facility. While also trying to defend his temporary hijacking of their systems that caused many to become paranoid about VEGA.

The slayer continues to look out into the frozen wasteland to kill time until his master wakes up.

"Ah! There you are!" A female voice calls out from down the hall. He turns around to find a young woman, who, he swears he saw her face somewhere before. She had dark brown hair, blue eyes and had a colourful attire that included a black gauntlet for the hand that held a staff.

The woman walks up to him, eyeing him up and down with great interest. She mutters a few things as she walks around the man.

"This is very interesting, your armour and weapons are very intriguing for a servant." She said. Of course, she was questioning the origin of the gear he carried, well who wouldn't in the current timeframe he was in.

"Well, you can't blame a scholar like me to be interested in a servant from a future era." She continued as if reading his thoughts. Wait for a second, how did she know he was from the future? Other than the fact some of the weapons looked like they could be out of a videogame.

"Vega gave us a basic understanding of where you two originated from. According to him you are some supersoldier bent on killing anything that threatened humanity. I think you will find yourself at home here with the current situation we are in." She said with the same positive tone

"Oh, where are my manners! I am the world-famous scholar Learanardo Da-vinci! Servant Class: Caster. I am currently summoned as the head engineer for Chaldea. But you can just call me Da-vinci chan." She said with a bow. The slayer just nods in acknowledgement and understanding that this woman was not a threat. The name did ring a bell but, like her face, can't put a finger on where he saw it before.

"Now with pleasantries out the way. I guess I should give you an update on our current situation…"

Da-Vinci explained to the slayer what was currently going on and the plan moving forward. First, most of the staff were killed by the bombs Leff planted in various places of Chaldea. Leaving them heavily understaffed and in shambles, as they try to get systems repaired to working order. Doom Slayer clenched his fist at the thought of more innocent lives murdered by that demon. Da-Vinci saw the withheld rage but continued to what the organization is going to do next. Thanks to Vega hijacking of the system, they were able to spot more singularities throughout the time that, if not dealt with within the next two years, could result in humanity being permanently incinerated. Time travelling? That was a new one for him, but was he a time traveller as well? He shook his head burying the thought of his origin...

"Is there a problem ?" She asked seeing the sudden head movement. The slayer just shook his head again saying no to her question. Looking at the time she decides to head back to her work.

"Well, it was nice meeting you. If you want to run some maintenance on your gear at any point during your stay here, feel free to stop by my workshop." She turns around to walk away but stops.

"Oh one more thing, I would appreciate it if VEGA would stop snooping around in our database. It's causing some of the staff to go on edge. But if he must...do it discreetly." She then smiles and waves as she leaves him alone. Sounded like Vega is going to get some getting used to for the people here. Well if Vega finds anything that the Slayer should know about, he won't stop him.

"Yes, it is an odd thought that Leonardo Da-Vinci, a male scholar and artist, would manifest with a female body if summoned as a servant. Along with said body looking like a life replica of his famous work: The Mona-Lisa" Vega said in his helmet. Doomslayer found it slightly odd but, then again, he also is a hell-walker that hops dimensions like it was Tuesday morning stroll.

"I will take her advice however and keep my attempts at gathering information more discreet. From what I can tell, she was recently summoned to help keep the systems running smoothly." The AI agreed to help the staff and Da-vinci get the place up and running for the next mission. The slayer just nods and returns to explore the place, generating an auto-map of the facility in the process for future reference. There was a chance that they could get attacked again by Leff and his forces so he wasn't going to take any chances.

Time goes on and the clocks show 8:00 am, Doomslayer didn't need to sleep so he found himself helping haul debris from the heavily damaged areas of Chaldea to keep himself busy. He got stares from the local staff as he picked up massive chunks of debris with little effort and tossed them into piles that were labelled "Possible Salvage" and "disposal". Once everything was organized a crew came in to fix the electronics of the Ray-shift equipment along with looking for salvageable parts. Dr Roman and Mashu came in following the crew and were amazed at how fast the area was cleared up and was confused at first but then found the marine standing out of the way to let the engineers work.

"Ah, Berserker. Good morning." Mashu said with a smile.

"I see you made yourself busy eh?" said amazed at the progress. With the area cleared they can get started on Ray-shifting sooner than expected. Doom Slayer nods and gestures to Mashu wondering how she was doing. There was a slight pause of confusion in communication as they did not understand what he was saying.

"He is wondering how you and the others are doing Mashu," Vega said, translating his gesture as he can read the slayer most of the time and understand what he wants.

"Oh, I am doing well. I am getting used to being a Demi-Servant and should be combat-ready for the next mission. Our masters are still resting as the Recent Ray-shift put some strain on their bodies." Mashu said

"Thank you for asking." Mashu nods. The man then leaves the room as the repairs continued for the next mission.

"He's an odd one but I am glad we have him on our side," commented.

"That's a rude thing to say, Doctor," Mashu said but then he corrected himself.

"W-what I am saying is that he is not a part of our recorded history, Just like Leff said." He corrected and She pondered at the thought of the Servant of Ritsuka. He's armour and weapons were confirmed to be more advanced then-current age firearms, even his double-barrel shotgun had a grappling hook that baffled some of the staff on its construction. Then there was Vega, the AI that is a part of the toolset is now integrating with the base's systems.

"Well, He isn't a threat and he seems pretty strong to be able to fight three servants one after the other. Doomguy is going to be a big help around here." Dr Romani smiles. This servant, even with his mysteries, is a godsend for Chaldea and humanity with the current situation

"I am glad he came, I can't imagine what would've happened to Ritsuka if Doomslayer-san wasn't there." Mashu eyes grew grim with worry for a moment but shake her head. No point in worrying right now, she was safe thanks to him.

" 'Doomguy?' where did that name come from?" She asked confused.

"Oh, Vega suggested it to give him a nic-name for the safe to make his presence here less fearful." Romani laughed a bit thinking how the AI suggesting such a name for a warrior like him.

"Doomguy-san...Yeah, that seems to make him more friendly sounding." Mashu laughs and smiles.

A Slayers Testament...

"In the first age, in the first battle, when the shadows first lengthened, one stood. Burned by the embers of Armageddon, his soul blistered by the fires of Hell and tainted beyond ascension, he chose the path of perpetual torment. In his ravenous hatred, he found no peace, and with boiling blood he scoured the Umbral Plains seeking vengeance against the dark lords who had wronged him. He wore the crown of the Night Sentinels, and those that tasted the bite of his sword named him... the Doom Slayer."

Ritsuka darts awake after a very strange dream...she looks around and finds herself in the room she was assigned to in Chaldea, that meant she was alive and made it back safely. Most likely the others as well...Minus the Director. Even with her disappearing, she was able to put on a proud face and push them onward. Ritsuka tried to strong there but was breaking down so fast seeing Olga dying before her eyes. She then thought about her dream...a voice was telling a story...all she could remember seeing was a symbol that looked like a sword striking downwards.

"Doom Slayer…"

Ritsuka shook her head, deciding to leave the questions for another time as right now she needed to find out what to do next. After getting out of bed and changing into her uniform, the novice master walks out into the hallway towards the command room. On her way there she finds Berserker staring at the snowy landscape through a window. She pauses for a moment just staring at the man who saved her life, her servant. A powerful warrior at the command of a mere novice like her...Ritsuka felt like she was being a dead weight to him. Her thoughts were then interrupted as his gaze moved onto her, acknowledging her presence.

"H-hey, Berserker…I um just got up and…" She stuttered with the sudden attention. He nods points to her and gives a thumbs up. She picked this up as wondering if she was alright.

"Oh, yeah I feel a lot better now. I just…" Her thoughts were filled with the dead city of Fuyuki and worries about the rest of the world.

"Is the world gone?" She looks out the window, beyond the snowy horizon. The slayer nods affirming that is most likely the state of this world.

"I see…"

It was up to a mere novice like her and Gudao to fight for humanity but is she up for the task? Back in Fuyuki, she was about to get mauled by monsters if Berserker didn't show up. How is a weak person like her going to fight in a war to save the world from destruction? How would she keep the promise the Direct entrusted her with.

As his master's thoughts raced in her head, her legs were shaking and her eyes looking at the floor. Doomslayer could see the panic that was going through the mind of the young one, it reminded him of the first moments on the Deimos base and his original encounter with the demons. The blood and gore that scattered the monster-ridden halls of that UAC base. He was a soldier back then, but Ritsuka was a rookie in a security organization and could practically be his kin judging from how young she saw.

Doing the only thing he knew to help her...He plops his hand on top of her head, lightly tapping her. His master looks up as she was taken out of her panicked state of mind and looks up with curious eyes. Doomslayer then moves his hand to her shoulder with a light grip. He points to her and then to himself and finally to the area around them. He was trying to say that she wasn't alone in this fight at all, she had Chaldea, her friends and himself alongside her in this fight. His master's eyes lite up and calmed down as she was able to read what he was trying to say. She took a deep breath as her legs stopped shaking and her will restores.

He will protect her at all costs.

"Thanks, Berserker...for everything." She smiles and the slayer responses with an offer of a fist bump. Ritsuka smiles and bumps her small fist with his armoured one.

"Alright! I am going to the command centre to check up on everything. See you later!" The magus said as she runs past him with renewed determination leaving Berserker behind with his thoughts.

"You have gone beyond my expectations on cooperating with master Ristuka. Then again she has not shown any reason to betray you." Vega commented as he was watching the whole conversation. Vega knew that the Slayer wasn't one for conversation or having someone command him. However, the AI found it curious that he was being so calm around the masters.

The Slayer rolled his eyes, he wasn't going to be an asshole towards the kids who could pass as his own. Their wills were strong and full of determination, Something that was lacking in his world. The UAC corrupted so many innocent lives...

"Would it be that you see them as innocents youths compare to the other individuals you met?" Vega asks and the slayer nods while making mental note on how well the AI was predicting his thoughts.

"I will make a note on this for future reference if that is ok with you"

The man just nods not caring what Vega does, he trusts the AI and that meant something for someone that as been alone warrior for aeons.

"Very well. I will continue assisting the staff and collecting any information that could prove useful in the future. It appears that Dr Romani is currently briefing the two masters. I would recommend joining them to boost morale." Vega then logs off and the Slayer decides to go to the command centre to see what was the next mission.

As he entered the room. The Dr was in the middle of explaining the situation to the masters. To put it simply, the two masters are the last hope for humanity as there were seven singularities in time that will cause the incineration of the human race. With the systems restore, they will travel back in time to fix these anomalies before it's too late.

"From now on Chaldea will follow through with former Directors Olga Maires plan to preserve the human race. Our goal is to protect as well to recover human history." Dr Romani said taking his position as the only person left to take the Director role.

"Our enemy is history itself. Many heroic spirits, who are legends, will be standing in our way" Ristuka looks over to Berserker after the mention of the legendary Heroic spirits but refocuses on the briefing.

"The only way to survive is to take back the future in this way. No matter what awaits us along the way." With the briefing finished and everyone gets ready for the first journey into one of the many singularities of this Grand Order. It will still take the rest of the day to get the systems online and has gone through the safety checks before they can begin Rayshifting once more. So, with that in mind, Both masters decide to assist the staff in preparing some supplies to be transported to them during the mission.

"So how are you holding up?" Gudao asked Ritsuka as he packaged some rations.

"It was hard earlier but Berserker cheered me up. Nothing is going to get done if we just mope around on our butts." She said as she moved on to the next supply drop.

"Good to hear. I am still worried about having Mashu fight but she seems ready as she can be. I'll have to do my best and back her up the best I can." He said with determination in his voice. Ristuka nods in agreement, even if they were novices, both can still learn and improve with experience.

"With Mashu on defence and Berserker on offence, we should be good for any fight." Ristuka smiles.

"Oh, you didn't get the word? During this mission, we are going to get to summon more servants to add us during our battles." Gudao said and Ritsuka eyes lit up in amazement. There would be more servants to help them out in this daring quest to save the world?

"R-really?! That's so cool!" She said with excitement.

"Yeah, I know, we'll need all the help we can get," he said, putting together the last pack of food rations and decides to take a break along with his fellow master. Chaldea plans to get the summoning system online so they can get send in reinforcements just in case.

The Shield and The Slayer.

Meanwhile, in the training rooms of the facility, Mashu was getting more experience in her servant form. Most of the techniques of the servant that is fused with her has become second nature to her, however, she could tell that some powers were a mystery to her. Along with the true name of the servant she is fused with

"I have to be strong, for my senpai's," Mashu said she deactivated her servant form to take a break from training. As the demi-servant walks out of the training room she was occupying she notices that the once across from her was in use. Curious she walks over to the observation deck that watches over all of the training facilities. She finds that Doom-guy was using it as a space to work on his arsenal. He had his rifle gripped arms on a table in pieces as the man cleaned them. Mashu, without thinking, enters the room and Doom-guy raises his head from his guns to acknowledge her.

"Oh-um Sorry I didn't mean to barge in um…." The man then raises his hand and shakes his head saying it wasn't an issue and returned putting his heavy cannon back together. Mashu continues to observe him as he worked on his gear, She was more curious about him being a servant more than anything. She was excited about meeting heroes of legend, including the man in front of her.

"Fou!" The little creature walks into the room with them as he is allowed to wander the place.

"Oh hey there Fou what are you doing here?" Mashu said looking at the little creature with a smile as he jumps onto her shoulder. It was hard to tell with the helmet but Berserker was watching fou with interest as Mashu offers him a treat. Wait a second, was Fou looking directly at him? No, there's nothing to worry about as he s probably just a leftover experiment of the place that turned into a pet.

After putting his heavy cannon back together he decides to test it on some targets. Mashu instant knew what to do and ran up to the nearest console.

"Ah, Here you go." She said as some firing range targets appear from the floor.

Berserker nods and proceeds to testfire both his Precision bolt and the Micro missiles. He first attaches the scope, aims down the sight and pulls the trigger. A larger bullet was fire from the cannon with a loud bang and destroyed the target and the one behind it. Satisfied, he swaps to his micro missiles pods barrel attachment. With a halving pull of the trigger, the pods open up with loaded micro rockets. The slayer then fires rockets onto multiple targets with them exploding shortly afterwards, leaving nothing behind. His arsenal works just like before but he now does not need to worry about ammo according to Vega. The perk of being a servant he guessed as he lifts his gun over his shoulder.

"Wow...Your arsenal is really impressive, Doomguy-san." She said amazed and letting his nickname slip out. He didn't react to it much, just a slight pause, but guessed it was Vega that suggested the name. Deciding that he was done testing his guns, for now, Berserker heads for the exit with Mashu following as well.

"Umm...Doomguy-san?" She asks a little sheepishly as he turns around.

"I...Look forward to fighting alongside you. I just want to apologize in advance if I am not up to par with you. I will do my best to keep up in a battle to keep our masters safe." Mashu said as she felt like she was inferior compared to him.

Doomguy shook his head and points to her then his exposed biceps and back to her. He was saying that she is strong in her way and just needed more experience. Mashu eyes lite up as she understood what he was saying and smiled at his kind words.

"Thank you, Doomguy-san. I needed that." She said with a boost in confidence. Berserker then gives her a thumbs up and walks away to go do his rounds about the facility.

"For a berserker, he seems very gentle. Eh? Fou?" Mashu said to the Fou on her shoulder who was still looking in the Slayer's Direction.

"Fou!" He yelped refocusing on Mashu and both go to get something to eat.

The next day…

Today was the day of the first rayshift to restore humanities future, Everyone involved with the mission was standing the command room getting brief on the location of the second singularity.

"Doing intensive research, we have confirmed that the enemy is going to be using holy grails to create these singularities as well as a form of transport to the targeted eras." Dr Romani said to the master as their coffins were prepped for rayshift. The primary goal is to retrieve the grails to shutdown the singularities and restore the flow of time. Just like how the slayer retrieved the one in Fuyuki which was a treasure trove of knowledge behind the singularities.

"Even if you correct history, Leaving the Grail will put us back to square one. You must either retrieve the Grail or destroy it." Romani stated the primary targets of there mission as there was an audible crack of knuckles at mentioning of the later and of course, the source of the sound came from Doomguy.

"Ahem, those are the two primary objectives of this operation. Is everything clear so far?"

"Yes!" The trio of youngsters said, ready for action.

Romani smiled and continued with the important tasks that must be done for Chaldea to assist inside the Era. Doomguy just tuned them out as he knew Vega would take care of it. All he was interested was where the enemy was and how much pain he was going to inflict upon them. He paused at the thought as he remembered that he also must keep his master alive during this whole operation. Mashu was a good fighter but she was still as green as the two masters. If things were his way it would only be him getting sent out into whatever hell these singularities were. However, they chose this path, and he wasn't one to choose there fates.

He won't let them walk the path of perpetual torment for it was only meant for him alone.

"Berserker?" Ritsuka calls out to him, adding him back into the conversation. It looks like Da-Vinci has joined the conversation and was carrying a backpack like an object.

"As I was saying, This is a carrier for a drone that Vega shall use as an additional point of data collection and tactical support." She offers it to Ritsuka who puts it on like a backpack. The drone itself looks similar to the onces Vega used to deploy newly developed weapon mods for the slayer mid-mission, but a lower-tech version and was white instead of green.

"It's a prototype but It's a wondrous mix of magic and science! Fresh from my workshop and ready for deployment!" She said with pride of an artist as she powered it on remotely and Vega connected to it.

"Connection established, I am now in control of the drone. I will begin diagnostics immediately, Leonardo." Vega said as his voice came from the drone currently docked on the pack Ritstuka was wearing. After some more introductions from Da-vinci to Mashu and the master, she leaves as fast as she came in.

With no time to waste they got ready for immediate Rayshift. Ritsuka, Gudao, Mashu and Doomguy got into the Coffins ready for them. This time their transport will be stable and controlled compared to what happened during the bombings. The lids of the coffins close and the system start to rayshift them to the disrupted Era in time.

The Slayer goes over the task at hand in his head:

Go back in time.

Kill whatever was threatening humanity.

Grab the grail.

Shutdown this singularity.

...and protect them at all costs.

AN: The Grand Order begins and The Slayer is ready to rip 'em up. Nothing much to report but expect Doomguy the be a much-needed boost for the Chaldea masters. How would the Servants of Orleans react to a titan of a man as he chainsaws wyverns? How well can he hold up to the Madness enhanced servants the servant, Jeanne Alter?

Anywho, I am going to tone down Doomguy's Chatterbox leaving him to communicate with actions. Which will leave more dialogue with Vega to keep up the mystery of the to the people of FGO.

...What would happen if she used True Name Revelation on Doomguy?

All will be answered in the next chapter: Knee-deep in Dragon's.