Orochimaru’s cursed seal is a forbidden technique which is designed to give its bearer more powerful chakra, transform their body and enslave them to his will. It contains his senjutsu chakra, a specially-engineered enzyme and a fragment of his consciousness.
The curse seal appears as three identical symbols in a circular pattern on the bearer’s body in its dormant state which then spreads across the body when activated. Unlike other juinjutsu, almost every individual with this cursed seal will have a symbol unique to them. However there are two symbols that are known to recur as they manifest only in the vessels who possess the greatest potential.
The Cursed Seal of Heaven appears in the strongest of those attuned to spiritual energy and the Cursed Seal of Earth appears in the strongest of those attuned to physical energy. These effects of these cursed seals are greater than the others but are equal to one another.
Orochimaru is the only person capable of branding someone with his cursed seal which he casts by injecting his chakra into the victim with a bite from his fangs and a unique hand-seal, a ritual similar to how the White Snake Sage of the Ryuuchi Cave selects his students for teaching senjutsu. After the branding, the victim falls unconscious as their body is forced to adapt to its tainted power. Only one in ten subjects are able to survive the process.
This is the first state of the cursed seal once activated.
It functions by absorbing the bearer’s chakra and the natural energy from their surroundings, converting it into senjutsu chakra through the consciousness within the cursed seal, and then pumping it back into their chakra pathway system to enhance their abilities.
The symbol of the cursed seal replicates itself to cover their body in its markings; how far the pattern spreads is in proportion to how much power the bearer is drawing from the cursed seal. One can achieve at least twice as much chakra of a higher quality, making their techniques more powerful and strengthening their physical capabilities such as their speed, strength and reflexes. It is a temporary but significant boost to their power that can allow them to fight harder and longer than they normally could.
However the cursed seal has its drawbacks as well as it is meant to invade the mind and body of the bearer. After it has first manifested, its presence leaves the bearer in constant pain for a time and it reacts whenever the bearer tries to release chakra to force its activation by drawing out more of their chakra regardless of their will. It requires an adjustment period for someone to consciously control the cursed seal’s activation without it acting against their will, something with depends on the bearer’s own strength of will.
Every time its power is released, the malignant spiritual energy hidden inside slowly erodes their will and stimulates their darker emotions to make them susceptible to Orochimaru’s control. An example of this control is that when he is nearby, he can make them suffer crippling pain through their cursed seal which leaves them helpless in his presence.
Once the cursed seal has invaded the bearer’s mind and body entirely, it evolves to the next stage of power known as Level 2 but at the cost of them forever losing their free will and becoming enslaved to Orochimaru.
This is the second and final stage of the cursed seal.
Once its contamination is complete and the bearer has fully adapted to senjutsu chakra, the specially-engineered enzyme that was injected at the moment of the branding is activated. This enzyme gives them to ability to automatically draw in natural energy themselves at a much faster rate and to a much greater degree but without the fatal consequences of holding too much of it inside the body. Achieving the second stage automatically increases the amount of power one can access even at Level 1.
When Level 2 is activated, the bearer’s chakra levels increase ten times over and the unbalanced senjutsu chakra induces a mutation known as the Cursed Seal Transformation. It enhances all of their physical capabilities such as their strength, speed, durability and stamina, grants them an altered physiology better suited for battle and raises the power of their ninjutsu, taijutsu and genjutsu and even their kekkei genkai beyond their previous limits.
The cost is that the strain of the transformation is far greater in comparison to Level 1 as the massive increase in power places a proportionate burden on their chakra system, leaving them exhausted as soon as they return to normal. The most skillful users can utilise partial transformations which take advantage of Level 2’s abilities without the full burden.
This state can be artificially induced using the Mind Awakening Pill. This is a drug that Orochimaru developed which overstimulates the cursed seal’s contamination rate to invade the entire body within seconds. However the no one is able to handle the physical stress caused by the sudden influx of power which causes the body to shut down and die.
To avoid this outcome, the Four Black Fogs Formation and Dark Sealing Method is used to soften that death to a temporary coma which gives the body time to adjust over several hours until the cursed seal evolves. However, in Level 2 the cursed seal’s corruptive influence is practically nonexistent as the consciousness within the cursed seal is no longer needed since the enzyme helps generate senjutsu chakra instead. This means that the bearer can reach the next level of power without the fear of losing their free will, unlike those who suffered through the entire contamination process.
Uchiha Sasuke, for example, retained his free will because Orochimaru’s desperation for a new vessel pushed him to evolve the boy’s cursed seal when it was still in the early stages.
Creating the Cursed Seal
Long before Orochimaru ever left Konoha, he learned about an old shinobi clan capable of powerful transformations similar to a kekkei genkai. When he conducted research about their power, he discovered that these transformations were controlled by a genetic cursed seal powered by natural energy.
He found the source of this power in the Ryuuchi Cave, the homeland of the summon snakes, and it was here that Orochimaru first signed the snake summoning contract just as Jiraiya found the toads in Mount Myoboku and Tsunade found the slugs in Shikkotsu Forest. Orochimaru survived the bite of the White Snake Sage which injected natural energy to test if he was capable of learning senjutsu, the original source of the Tenbin Clan’s power. He learned to create senjutsu chakra but his body wasn’t strong enough to truly harness it and bring out its full potential.
This is partly why Orochimaru sought immortality by transferring his soul from one body to another as a more powerful body would allow him to achieve a true Sage Mode. Until he was able to create his immortality ninjutsu, he chose to develop an alternative method of harnessing senjutsu based on the Tenbin Clan which would induce an artificial type of Sage Mode in the subject.
Orochimaru tested the prototype cursed seal on ten individuals to see if it worked. Only his student Mitarashi Anko survived as proof that only one in ten were capable of surviving the branding. That was one of the last experiments Orochimaru conducted as an official shinobi of Konoha.
Anko’s cursed seal was studied by Konoha extensively but they couldn’t figure out a way to remove it without killing her. The only one who might have been able to divine more about its nature was Jiraiya but he was preoccupied in chasing after Orochimaru who had defected. Instead, the Third Hokage sealed it himself.
Konoha was eventually able to develop the Evil Sealing Method as a counter for juinjutsu, preventing it from affecting the bearer without them willingly seeking to use its power. Though by that time, Anko had been protected from its effects for long enough that it had been forced into dormancy and thus didn’t require the seal herself.
Years later Orochimaru found Juugo, a young boy who was the last known descendant of the Tenbin Clan. He extracted Juugo’s bodily fluids and used them to refine an enzyme that would strengthen his own cursed seal with the boy’s chakra and induce similar transformations in its subject.
This perfected version of the cursed seal appears to function just like the prototype cursed seal which misled those who saw Sasuke’s cursed seal into assuming it was the same as Anko’s. Thus they never discovered that it was actually far more powerful and influential and had the potential to evolve to another level. Fortunately, Sasuke was nevertheless protected by the Evil Sealing Method which played a vital part in stopping him from being consumed by its power or Orochimaru himself.
Ideally, Orochimaru’s vessel would have possess a naturally strong body that comes from a powerful bloodline such as the Kaguya or the Uchiha, and would have been corrupted by the full evolved cursed seal to provide a body capable of using senjutsu and remove any resistance against the Living Corpse Reincarnation. But Kimimaro’s sickness and Sasuke’s defiance prevented that ideal from ever being made a reality.