"For those of you who have returned in the hopes of seeing this story been given a proper update, I must unfortunately inform you that this is not the case. Author-san had lost interest in the Jujutsu Kaisen series some time ago, and thus will not be returning to this fic in any meaningful way. But do not despair, for there is a glimmer of hope to be found should you desire reading a story similar to this. The fanfic author Nnathann has gone about creating his own story using MementoMori's as a basis. It is called Curse of Justice, so go and give it a read. As for what follows, Author-san has compiled various story ideas, plot-threads, and unconnected scenes that he had planned for The Cursed Armory, but ultimately dropped. He has already given permission to Nnathann to utilize anything that follows for their own story, so anyone else is free to take what they wish and turn it into their own fic. Best of luck in your endeavors should you choose to pick up the torch."
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When I first began writing this fic, I couldn't quite decide where I wanted to introduce Shirou into the JJK timeline. I had already decided on a failed Heaven's Feel route for his character but chose to maintain a bit of ambiguity behind how the two series connected, as there were a few reasons for this. The first concerned when the series' took place, as there is a bit of a time-gap. Next was how to combine them in a manner that didn't feel clunky. Straight-up alternate reality traversal felt a bit forced and cliché, so my other choice was AU. The jujutsu sorcerers would essentially be a branch of magi who held loose relations with the Clocktower and such, and they served a similar purpose to a Burial Division.
You've already seen how I initiated the connection between the two series by having Shirou combating a Curse born from Sukuna's finger. The idea I had was that after Fuyuki, Shirou is left with nothing. He had forsaken his ideals -his promise to his father-, but he still couldn't save those he cared about the most.
"What was once an idealistic promise to his dying father, eventually revealed itself to be a curse. A restriction to his life that prevented him from truly living. But by the time he realized this and chose to break the shackles, it was already too late."
His ideals thrown away, everyone he ever cared about now dead, and with Archer's arm slowly trying to kill him, Shirou simply wandered the land with no real purpose. Though death would reunite him with those he cherished, he felt he hadn't yet earned that kindness. And so he marched on, helping those in need until the day came where his body finally gave out and granted him his eternal rest.
As for when in the JJK storyline I wanted to introduce Shirou, it was a bit of a tossup. Itadori's 'death' was something that needed to happen, but I had to be careful as to Shirou's inclusion should it be prior to the mission where Itadori died. The first route I settled on was having him get separated with Kugisaki. After he, Kugisaki, and Fushiguro manage to escape from the building, things proceed as normal with Itadori. Due to having him as backup, Kugisaki is not as severely injured as normal, but she and Shirou are still sporting some wounds. All three are still present when Sukuna makes his appearance, at which point he proceeds to taunt them. Fushiguro states his intention to remain behind since he is in the best condition and hopes to keep Sukuna occupied for as long as he can while the other two escape. Shirou naturally turns down the offer, stating that running would be pointless. Having already been briefed on the danger that Sukuna poses, Shirou could tell that the Curse could kill them whenever he wanted, so the better option would be to fight together. Kugisaki reluctantly agrees, as she refuses to be the coward who gets stabbed from behind. Sukuna gives them a single mocking clap, applauding their logic, stating that he would have killed them the moment they turned around, as he prefers to look his victims in the eyes when he kills them.
While not quite as much of a curbstomp on Sukuna's part, the valiant resistance the trio put up is ultimately worthless. Shirou, deciding that now would be as good a time as any, decides to put everything on the line. Instead of Fushiguro stepping forward to begin initiating his ultimate summon, Shirou starts to loosen the shroud and prepares to make an attempt at manifesting his Reality Marble. His logic is that all three of them are basically dead at that point. Sukuna has them cornered and beaten, and the only thing stopping the curse from killing them outright is his amusement at seeing them squirm. While it would most definitely kill him as a result, Shirou knows he's dead even if he doesn't do it.
Sensing something interesting coming, Sukuna begins paying rapt attention to Shirou as he begins his aria. After saying the first line, Sukuna has a similar reaction to the original scene with Fushiguro, causing his concentration to lapse just long enough for Itadori to take back control.
Halting himself from going any further, Shirou manages to wrest control back from Archer's arm before it's too late.
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That was my first option for how I wanted the story to begin. The second route I planned was having him be introduced as the new student after Itadori 'dies'. Essentially the mission where Shirou encounters Gojou, is the same mission that the man was away on when Itadori was killed. Both Fushiguro and Kugisaki make disparaging remarks to their sensei, asking if the man had already grabbed a 'replacement' for their fallen friend. Gojou naturally laughs this off and such, stating it was a pure coincidence, but that they are free to think what they want. There would then be a few follow-up scenes where they get to know each other, train, and meet the second-years.
During the initial encounter where the Kyoto students come to harass everyone (meaning Todou and Zenin Mai show up), I had planned to have Shirou be helping out the second-years at that time, only showing up towards the end of the fight between Fushiguro and Todou to stop the conflict. Seeing as how this will be Shirou's first encounter with Todou, the latter poses the same question that he did to Fusiguro.
"What's your type of woman?"
Shirou, equal parts surprised and confused at the seemingly irrelevant question, fails to immediately answer. Upon Todou providing further clarification, Shirou understands what he is being asked, and decides to humor the man with an answer.
"I don't have a type…" he responds with a slightly somber tone.
Todou begins to grow irritated with such a lackluster response, only to settle down as Shirou continues.
"I don't have a type, because I had already found the one whom my heart belongs to. I was a fool back then, taking for granted her kindness, her smile. It wasn't until the happiness we shared was destroyed, that I finally realized how blind I had been to everything around me." looking off into the distance, Shirou could just about visualize that smile upon the blank canvas of the sky. "My heart belongs to her. And though she is gone, it will forever remain that way, for I know she is patiently waiting for me to one day join her. The day when she smiles and once more greets me as 'senpai'."
There is a moment of silence as a stone-faced Todou calmly walks up to Shirou, pausing his steps just within arm's reach. The older teen then raises a resolute fist and slowly but firmly presses it against Shirou's chest. He then turns and walks away, a look of nostalgia in his eyes
"Until we meet on the battlefield, my old rival…"
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At the start of the exchange festival, I planned to have a few minor interactions, such as Shirou offering up the use of some of his traced weapons for anyone who wants them. The majority of these first few scenes would have varied depending on if I chose to introduce Shirou now (as this would now be his first encounter with Itadori) or at the earlier option.
The story would then proceed mostly as canon, but I hadn't decided where to put Shirou during the first skirmish. I then planned to have him join the battle against Hanami towards the end of when Fushiguro is fighting. With first having Shirou as backup and Itadori and Todou joining in soon after, the wounded students fall back, but not before Shirou hands off a copy of Rule Breaker, stating that it should be able to dispel the barrier keeping Gojou out, provided the blade makes contact with it. What follows would then be a chaotic three versus one battle against Hanami, with Todou being quite excited at the prospect.
"With my brother to my left, and my rival to my right! This will be a battle for the ages!"
Seeing as how Todou can utilize his technique on objects with cursed/magical energy, he instructs both Itadori and Shirou to not pause in their attacks not matter what, as he will handle the strategy. Being able to provide his allies with weapons, as well as scatter them across the battlefield for Todou to utilize as 'warp-points', the trio are able to overwhelm Hanami with ease.
The barrier comes down sooner than usual, as Rule Breaker was passed to Nishimiya, who was able to quickly reach the edge of the area. With Gojou being freed to act at an earlier point than planned, 'Geto' is forced to have Mahito retreat before acquiring Sukuna's fingers, only having enough time to find the cursed embryos.
When all the dust settles and the enemy force is defeated, Shirou walks over to grab a bit of branch they managed to chop off of Hanami's 'eyes'. He then explains that by using the branch, he can track down the Curse no matter where they are. I planned to have this revelation speed up the time table, as since Gojou is still in play and the enemy haven't finished their preparations to trap him, it means that the 'final confrontation' is almost upon them.
Some time would then be spent for slice-of-life-type scenes, before all of their forces gather and prepare to attack the enemy hideout. It is highly unlikely that 'Geto' could have predicted Shirou's ability to track them, and Mekamaru would not inform them, considering victory is pretty much assured with this.
I hadn't quite decided how the events of the final battle would take place, but I would have to take into consideration that the brothers who would have fought Itadori and Kugisaki would still be alive for the fight.
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Next is just a variety of ideas and concepts that I wanted to make use of.
The Juuichi Yosamu, a sword that Shirou can trace, bears a curse, so I wanted to make use of it at some point.
Gae Bolg was difficult for me to think about including, as Cursed Spirits don't die just from having their hearts destroyed.
Gae Dearg and Gae Buidhe abilities would be considerably useful against the 'top tier' Curses. Jogo, Mahito, and so on.
Inumaki would start saying ridiculous onigiri ingredients after trying Shirou's food. Things like, caviar, bacon, truffles.
I would imagine that Sukuna would take interest in Shirou, considering both of their 'souls' are so similar. Shirou is a sword, whereas Sukuna is a Curse that cuts. 'The tool, and the action'
I had a fitting end planned for Mahito, where his opponent ends up being Shirou. We all know that Mahito gets off on tormenting others -Itadori in particular- and would no doubt jump at the chance to kill one of his allies in front of him. I was thinking something along the lines of Mahito fighting Shirou, but not giving it one-hundred percent immediately. He waits for/leads the battle towards Itadori before going in for the kill. His method of choice being the same tactic of touching the person to alter their body. However, unlike what normally happens, Mahito suffers a similar rebound to what Sukuna does. Whether it's because he happens to make contact with Archer's arm or just because Shirou's soul is already a sword, the 'Human Curse' Mahito is not only rebuffed, but is attacked in return. The thought process behind this encounter is that Shirou is not exactly 'human', at least not in the spiritual sense. The concept of Shirou's identity is Sword, while the concept of Mahito's identity is Human. Mahito is able to manipulate the bodies of others because he is reshaping the 'human soul' the possess, as that is the nature of him as a Curse. Thus Mahito is unable to transform something that does not match the material he is able to work with. Overly simplified, it's very much a case of square-peg and round-hole.
Regardless, swords begin to violently erupt from Mahito's arm before he quickly severs the limb to halt the influence of Shirou's soul. This essentially means that both Itadori and Shirou are immune to Mahito's curse, or rather, it's too dangerous for him to use on them directly.
I never decided whether or not to fully utilize Shirou's Reality Marble, as given his condition, it would most certainly result in his death, essentially ending the story (at least from the crossover perspective).
"I have a technique that can definitely defeat him, but it will come at the cost of my life. Just keep him busy for sixty seconds. I need time to prepare."
The only opponent I can think of who Shirou would need to use this against would be Sukuna himself.
I also contemplated having Shirou snipe 'Geto' from a distance while Gojou keeps him distracted. I would imagine a Black Key or something along that line altered into an arrow-form would likely kill the Curse with a headshot. With the Curse dead, Geto's followers would probably stand down -at least the ones who were fighting for the sake of having their masters body released-, while the remaining Curse's will be left with no one to give them further direction, destroying any cohesion they had as they try to formulate a plan of action, whether it be to escape or rampage.
There is also one situation I could think of to have the story end with a battle to the death between Shirou and Sukuna, where Itadori wouldn't have to die as a result. In the Fate series there is a character named Suzuka Gozen, who possesses a sword called Kenmyouren. It's a bit confusing to understand, and you might want to look it up yourself, but the sword has the ability to 'create parallel worlds within it'. The idea being that Shirou uses the sword to create a miniature temporary reality where he can draw Sukuna in to fight. By stabbing the sword into Itadori (mind the vitals!), Shirou is able to force Sukuna's soul into the sword. Shirou would then enter the sword himself, albeit not physically. Think something along the lines of a battle in the mind, but instead it is two souls clashing against one another in a sword.
That's pretty much everything I got. Sorry about letting you all down, but Jujutsu Kaisen just wasn't the story for me, so I lost interest in it.
Again, I recommend you check out Curse of Justice by Nnathann if you want to read something similar.