This post is gonna be 1 of 3 where I come up with theoretical curse technique reversals for every technique in the series, starting with everyone at jujutsu tech. Every technique will have a reversal that has a unique, hopefully useful effect (so no techniques where the reversal just doesn't do anything) and a "hollow technique" like Limitless' purple where you combine both the original and reversal. For techniques without official names I used the ones given on the wiki

Straw Doll Technique (Nobara Kugisaki)

Resonance → Dissonance

Attacks on the user or their straw doll will have their damage mirrored back to the attacker, moreso if they hit the actual user instead of the straw doll.  Does not prevent the user from taking damage, only causes the attacker to receive the damage as well

Hollow Technique

Allows for simultaneous usage of curse technique and its reversal

Hairpin → Hairclip

Causes the cursed energy imbued within the user’s nails to implode, pulling things in

Hollow Technique: Nail Bomb

Cursed energy imbued within nails simultaneously explodes and implodes, forming an effect like Limitless’ Hollow Purple around the nails, though weaker

Ten Shadows → Ten Stars (Megumi Fushiguro)

Instead of using shadows as a medium for summoning shikigami, the technique uses light as a medium.  This also lets the user manipulate light which can be used in dark areas or for blinding opponents

Shikigami: 

Divine Dogs → Divine Panther

Stats:

AP: High (> Divine Dog Totality)

Speed: High (> Divine Dog Totality)

Durability: Medium (< Divine Dog Totality)

Faster and has stronger attacks than Divine Dogs, but has less durability.  Can be used without being tamed like Divine Dogs

Toad → Tortoise

Stats:

AP: Very Low

Speed: Extremely Low

Durability: Very High

Can slow down anything in a radius around itself, allowing the user to prevent escapes and neutralize projectiles

Great Serpent → Great Eagle

AP: High

Speed: Very High

Durability: Low

Is summoned from the sky and will dive bomb its target.  Can also be used to grab people.

Nue → Namazu

AP: Medium

Speed: Medium

Durability: High

A large catfish which can move underground and cause violent vibrations able to stun people or cause earthquakes

Max Elephant → Swarming Insects

AP: Medium (Main Body) / Low (Summons)

Speed: Medium / High

Durability: Medium / Very Low

A large fire ant which is able to summon swarms of smaller ants similar to Kurourushi.  Ants leave burn marks on bite which take longer to heal

Rabbit Escape → Komodo Armor

AP: High

Speed: Low

Durability: Very High

A large, hollow komodo dragon able to freely separate and reconnect parts of its body.  The user can wear the body parts for extra protection or use the komodo’s fangs to deal more damage and inflict venom

Piercing Ox → Striking Bison

Stats relative to Piercing Ox

Runs in a curved line until it rams into its opponent, the longer it takes to reach its target the less damage it does

Round Deer → Spiked Bear

AP: High

Speed: Low

Durability: High

Emits a cursed energy aura that harms opponents and buffs allies’ output

Mahoraga → Marici

AP: Extremely High (= Mahoraga)

Speed: Extremely High (= Mahoraga)

Durability: Extremely High (> Mahoraga)

A large humanoid with bird-like features.  It possesses a bow on its arm capable of shooting arrows which have a similar effect to the Angel’s technique, nullifying techniques it comes into contact with and ripping through cursed energy reinforcement (Not full dura-neg but partial).  It does not have Mahoraga’s wheel of adaptation or regeneration

Cursed Speech → Cursed Actions

User can apply technique to anyone within their line of sight, while it is active the user will narrate all the target’s actions.  This persists even after line of sight is broken.  The normal snake eyes and fangs tattoos are replaced with hawk wings and beak

Hollow Technique: Looping Curse

The user’s narrations now become cursed speech instructions as well, causing an infinite loop of commands.  Backlash is reduced on narrated commands (so the first command given will have normal backlash and all the ones caused by the reversal will have lessened backlash)

Credit: u/PriorPossible834

Copy → Paste (Yuta Okkotsu)

Allows the user to ‘paste’ a technique, temporarily removing it from their arsenal and giving it to someone else.  Requires physical contact to transfer techniques

Hollow Technique: Datamosh

Simultaneously copies the target’s technique while pasting another one, causing the technique’s ‘information’ to get jumbled together.  This creates a new merged technique in the user’s storage and temporarily lets the paste target use the merged technique

Credit: u/Rothariu

Private Pure Love Train (Kinji Hakari)

Transforms the luck-based pachinko domain into a more skill-based basketball themed domain.  When applying his curse technique reversal to his domain it manifests as a gym basketball court where he enters the jackpot state if he scores 3 consecutive baskets.  Using the reversal outside of his domain allows him to manifests objects from the domain like his normal technique

Hollow Technique

Allows for simultaneous usage of curse technique and its reversal.  Cannot apply both to a domain expansion

Love Rendezvous (Kirara Hoshi)

Reverses the order objects must go in to approach other stars

Hollow Technique

Requires you to follow both routes at once, making it impossible to approach other stars at all

Pain Killer (Arata Nitta)

Prevents any wounds the target has from healing unless reverse curse technique is used

Hollow Technique

All wounds affected by the technique are unable to get better or worse

Construction → Deconstruction (Mai Zenin/Yorozu)

Converts nearby matter into cursed energy.  The amount of cursed energy gained is equal to the amount that would be needed to create the matter.

Hollow Technique: Conversion

Using construction and deconstruction at the same time lets the user directly change matter however they see fit

Puppet Manipulation → Mind EMP (Kokichi Muta)

Allows the user to pass control over their puppets to another person.  To those who without a similar technique (like Black Bird Manipulation) the sudden stream of information from the puppets will overload their brain.

Hollow Technique

Allows for simultaneous usage of curse technique and its reversal

Blood Manipulation → Vein Hijacker (Noritoshi Kamo/Choso/Yuji Itadori)

Allows the user to manipulate other people's blood externally or, as long as they are in contact with them, internally.  Requires the user to imbue the blood with their own CE before controlling it, meaning they cannot immediately control all the blood in someone’s body when making contact or fresh blood from a wound

Hollow Technique

Allows for simultaneous usage of curse technique and its reversal

Boogie Woogie → Show Stopper (Aoi Todo)

When the user claps a targeted object freezes in place, it will unfreeze when they clap again, maintaining any momentum it had or gained from being acted upon while frozen.  People and curses can break out of the freeze prematurely while overriding the momentum from the freeze

Hollow Technique: Encore

Freezes an object and attempts to swap it one clap.  When the object is unfrozen it will fly at incredible speed toward the object it would’ve been swapped with.  Can also freeze both objects in the swap, meaning the next clap will unfreeze both causing them to fly toward each other at high speed

Tool Manipulation → Tool Freeze (Momo Nishimiya)

Anything considered a ‘tool’ by the technique is frozen in place and unable to be moved.  Tools will continue whatever trajectory they were on before being frozen once unfrozen, and they will not gain any momentum from being acted upon while frozen.

Hollow Technique

Allows the user to selectively choose what tools to manipulate and which ones to freeze

Sound Amplifier (Gakuganji)

Decreases all sound from the user, making them completely inaudible

Hollow Technique

Simultaneously imbues sound with cursed energy while making it inaudible, creating an invisible, silent attack

Solo Forbidden Area → Challenge Arena (Utahime Iori)

Decreases the cursed energy efficiency and output of targeted sorcerors around the user

Hollow Technique

Allows simultaneous usage of curse technique and its reversal

Ratio → Whole (Kento Nanami)

Damage to any spot is equally distributed throughout the surface of the target’s entire body.

Hollow Technique: Distribution

Allows the user to get critical hits while distributing the damage across the target's entire body

Auspicious Beasts Summon → Auspicious Beasts Conjuring (Takumo Ino)

Allows the use of an mask as a spiritual medium without needing a wearer, allowing the user to summon the auspicious beasts as their own shikigami rather than just summoning their abilities

Hollow Technique

Allows simultaneous usage of curse technique and its reversal.  User cannot use the abilities of the beasts they have summoned as shikigami

Black Bird Manipulation → Mind Murder (Mei Mei)

Allows the user to pass their ability to control crows over to another person.  To those who without a similar technique (like Puppet Manipulation) the sudden stream of information from the crows will overload their brain.

Hollow Technique

Allows for simultaneous usage of curse technique and its reversal

Star Rage → Speeding Comet (Yuki Tsukumo)

Adds negative virtual mass to the user, causing them to become lighter.  This increases their speed while having no effect on the force they apply to objects.  After a certain threshold the user will die if they make themselves any lighter

Hollow Technique: Event Horizon

User can add positive and negative virtual mass without them interfering with one another, allowing for both high damage attacks and high speed movement.  

Immortality → Mortality (Tengen)

Prevents user from physically aging but does not increase their lifespan

Hollow Technique: Ascension

Prevents user from physically aging as a human while keeping immortality, but quickens their evolution into a cursed spirit