Domain Expansion

Domain Expansion is an advanced barrier technique and is considered the pinnacle of jujutsu sorcery. It constructs the user's innate domain inside a barrier infused with their innate cursed technique. Within a domain expansion, the user's cursed techniques are improved and any that are activated are guaranteed to hit.

Description
Domain expansion is the most supreme technique of any jujutsu user. It is achieved by expanding one's innate domain with cursed energy while using a barrier to construct it inside a separate space. The caster then imbues their cursed technique within the barrier to complete the expansion, allowing them to deploy their ability all throughout the domain.

A specific hand sign or signal unique to the user is required to expand someone's respective domain. From the outside, a domain's barrier is normally completely closed, making it appear as a floating black sphere that can even be moved slightly if needed.

Lethal Domains
Domains that are expanded to be lethal are constructed within a barrier imbued with the user's cursed technique. The caster's abilities are amplified and any cursed techniques deployed within the domain are guaranteed to hit their target. This sure-hit factor is derived from the barrier's embedded technique, which is what makes this type of domain considered lethal. These can't-miss attacks can't even be stopped by Satoru Gojo's Infinity. However, not all guaranteed hits are necessarily lethal. Kinji Hakari's domain technically possesses a sure-hit function, but it only transfers information to its target in exchange for faster technique activation and strength in a clash of domains.

Lethal domain expansions require immense skill and cursed energy to construct. Not only do they require the user to manifest a massive artificial environment, but they must be able to erect their own barrier and infuse it with their cursed technique in a timely fashion as well. Megumi Fushiguro for example, cannot expand a completed lethal domain because he struggles to create an independent space using a barrier.

Without enclosing the barrier and infusing it with his cursed technique, Megumi's domain doesn't have a guaranteed hit. Due to the overall difficulty of casting a lethal domain, the ability to expand a lethal domain is extremely rare, and even most grade 1 sorcerers are never able to master it.

Only Sukuna and Kenjaku possess the ability to expand a lethal domain without enclosing their barrier. Their barriers possess no outer shell yet still retain a sure-hit. It is akin to painting on air instead of a canvas and is remarked as divine, even by the standards of domains.

Non-Lethal Domains
In the past, Domain Expansion was a more common technique because domains weren't constructed to be fatal. They only forced targets inside to obey the rules of the embedded cursed technique. As more domains were constructed to be lethal, the number of users greatly decreased over time. Hiromi Higuruma's Deadly Sentencing is an example of an old-style, non-lethal domain that forces his opponent into a trial.

Incomplete Domains
Innate domains that are expanded using only cursed energy without an embedded cursed technique are incomplete even if they include a barrier. In most cases, the same applies to domains without a fully enclosed barrier. Closing the barrier fully integrates the embedded technique into the domain and enables its sure hit effect. Without that, the caster will only receive an improved cursed technique without a can't-miss attack. Barriers forcibly enclosed using the shape of an outside environment also do not incorporate can't-miss attacks.

Drawbacks
A high-risk, high-reward maneuver, Domain Expansion provides a great advantage at the cost of an immense amount of cursed energy. Satoru Gojo is considered to be one of the only individuals that can use domain expansion multiple times in one day. Kinji Hakari is only capable of casting it repeatedly after hitting his domain's jackpot to replenish cursed energy and stabilize his cursed technique.

Even if the barrier or the environment aren't fully formed, casting domain expansion will cause the user's innate technique to become unstable for a short time afterward. Attempting to use cursed techniques during this period will cause them to burn out and fail to activate.

Countermeasures
A domain's can't-miss attack can sometimes be countered with cursed energy reinforcement, but this is an impractical method. The only true defense against can't-miss attacks for those who cannot expand their own domain are anti-domain techniques. New Shadow Style: Simple Domain and Hollow Wicker Basket neutralize the barrier's embedded technique in order to nullify the guaranteed hit function.

Domains are nearly impossible to escape from the inside. The cubic volume of the space appears completely different on the inside, making finding the boundary's location difficult for anyone trapped inside. Anyone searching for the edge of the domain is likely to be killed by its can't-miss attack and the barrier is reinforced from the inside even if they did find it. However, the more the barrier is reinforced from the inside, the more vulnerable it is to penetration from the outside. In specific situations, an ally of the domain's target can break in from the outside to rescue them.

Domain Clash
The best countermeasure against an opposing domain is to expand one's own domain. This will engage both combatants into a clash of domains where the more refined domain will conquer. The time it takes for one domain to dominate in a clash varies on that difference in refinement. E.g. Satoru Gojo's superior domain immediately dominated Jogo's while Dagon's domain took a much more significant amount of time to subdue Megumi's. In the case of overlapping domains, sure-hit effects cancel each other out. When two domains are completely even and the users fight with their domains open, the moment one combatant takes heavy damage or their domain collapses, the other's can't-miss attack will immediately strike. A clash of three domains is even more complicated than two and too many conflicting factors can cause the barriers to shatter before the domains are completely formed.

Domain clashes don't always have to result in one domain conquering the other. Using Domain Expansion against a more refined domain can create a hole in the barrier for them to escape from as well.

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