Power of the Titans

"What are you? A man? Or a Titan?"

- Kitz Weilman to Eren Yeager

Titan shifters are humans in possession of the power of the Titans (巨人の力) which allows them to transform into Titans. Unlike regular mindless Titans, they are able to control their form and retain their human intelligence. It is often noted that these Titans are far more powerful than regular Titans and oftentimes display abilities unique to only them, though only nine humans can possess the power of the Titans at any point in time.

Transformation
In order to transform, a human with the power of the Titans must suffer an injury that draws blood (often self-harm) while having a solid goal or belief in mind at the moment of injury. However, being injured by another person is also sufficient. Once the transformation is initiated, a burst of energy is released (in some cases as a bolt of lightning or an explosion), followed by the generation of the Titan body and a release of hot steam. After transformation, the human body rests within the nape of the Titan's neck, the center of control. The human body is also merged with the Titan's flesh inside to varying extents, most frequently on the area of the cheeks below the eyes, rendering them immobile.

If a Titan form is pushed to its limit, the human will emerge from the nape of its neck, sometimes in a semi-conscious or entirely unconscious state. But if a Titan form is not exhausted, then its human form can emerge from the Titan form in full consciousness. In some cases, a human is able to partially emerge from their Titan body without fully leaving the nape.

When the power of the Titans is used, oftentimes the area around the emerging human's eyes is marked by dark lines for a short time after. The amount of time the human possesses these marks appears to depend on how long, skilled, or overworked they used their Titan forms, ranging from several minutes to several hours.

In some cases, the ability to transform into a Titan is hindered by injuries inflicted on the human body. A human can transform into a Titan with injuries as severe as a missing limb, but only if a previous transformation has not occurred recently. If a human emerges from their Titan form and receives severe injury, this person cannot transform into a Titan again until said injuries have fully healed.

Humans with the power of the Titans appear to be resistant, but not immune to, the normal absorption that creates mindless Titans if they stay transformed for long or repetitive periods of time. In the case of Eren Yeager, it has been shown that repeated transformations in a short period of time lead to decreased control over the Titan form, as well as diminished Titan size and power. As such, it seems that there is a limitation on how long a human can remain in a transformed Titan state before risking absorption. The length of time spent in a controllable transformed Titan appears to depend on how skilled the human is at controlling their Titan form. However, even the most skilled humans with Titan power can become incredibly fatigued for as long as several days after repetitive use.

Physiology and abilities
The average height among the transforming Titans is 15 meters, but this can vary greatly, ranging from the 5 meters of Ymir's Titan form to the 60 meters of the Colossus Titan. It is notable that the female Titan forms have thus far been shown to be shorter than the male Titans, with the Female Titan standing at 14 meters and Frieda Reiss' Titan form being 13 meters tall. Humans with the power of the Titans also gain the Titans' ability to regenerate and are capable of vastly improved healing abilities, even to the point of regaining lost limbs. However, regeneration from severe injuries such as lost limbs can strain their powers and prevent them from transforming for a period of time. It is evident that healing for a Titan's human form takes much longer than their Titan form. The time it takes to regenerate appears to depend on the extent of the injury and how focused the individual is on healing that area. The only surefire way to kill a human with the power of the Titans is through severing the brain's connection to the rest of the body, although on rare occasions the most skilled humans with the power of the Titans are able to transfer their minds to the rest of their nervous system and survive even this.

It is also shown that these Titans are not safe from regular Titans, and will be attacked even while transformed. This is because Titans are regular humans that have been transformed into uncontrollable Titans, and the only way for a Titan to regain its human form is by eating a human with the power of the Titans.

While not all Titan abilities have been identified, each inheritable Titan possesses a unique power. Bertolt Hoover has been shown to possess significant control over his Colossus Titan body, able to release devastating gusts of steam to ward off enemies or even completely evaporate his Titan form in seconds. Reiner Braun's Armored Titan possesses hardened armor-like skin covering all but the key areas of movement. Annie Leonhart's Female Titan is able to call upon mindless Titans with a scream, luring dozens towards her position with little time. Zeke Yeager's Beast Titan is able to control Titans to a small extent, and there is evidence to suggest that the Beast Titan is able to turn Eldians into Titans without the use of Titan serums and can store these Titan bodies in invisible paths at his discretion. The Founding Titan has historically been the greatest of all Titans, able to have complete control over the actions and memories of Eldians, both human and Titan.

Some Titans have been shown to possess the ability to harden their skin to the point of near indestructibility. The most notable Titan in possession of this ability is Annie's Female Titan, which is able to selectively harden regions of her Titan body and even create a hard crystal around her human body, putting her in an apparently unconscious state with no need for nutrient intake. In addition to the armored plates covering Reiner's Armored Titan, he too is able to control some hardening aspects of his Titan such as creating claws on his fingertips. Zeke Yeager's Beast Titan also possesses a hardening ability, though it has not been seen at use. It seems, however, that not all transformed Titans possess this hardening ability, as Eren was unable to cause his Titan to harden until he ingested an "armor" Titan serum.

Inheritance
A human's ability to transform into a Titan can be transferred to a new host, should they be devoured by a mindless Titan. This allows an ordinary Titan to become a new human with the power of the Titans. Furthermore, the abilities of each Titan are also inherited by the new Titan, as has been the case with the Founding Titan for over a thousand years. It is also known that humans with the power of the Titans can gain new powers by consuming a specialized Titan serum, as Eren consumed a bottle from Rod's bag labeled "Armor" which gave his Titan form the power of hardening its skin at will as other Titans are able to.

It must be noted that transformed Titans do not seem to adopt the Titan form of the Titans they consume, as both Ymir's and Frieda's Titan appearances remained relatively the same before and after eating Marcel and Mr. Reiss, respectively. Rod Reiss has claimed that humans can choose the serum that will give them a specific Titan form, meaning they are able to adopt the form given by the serum and not whatever form the Titan they eat possesses.

However, some Titan forms do seem to experience certain changes. Eren's original Titan form just after receiving the serum was much smaller and seemingly less mature than his current form, and both Ymir's Titan form and Frieda's Titan form were noticeably more emaciated than their Titan bodies after gaining the power of the Titans. Nevertheless, the most noticeable physical features of each Titan were present before and after the inheritance of the power. Whether this is correlated to the aging and training of the human form, or a side effect of eating a Titan, is unknown. It is also noteworthy that the Titan forms of Reiner and Bertolt did not experience any noticeable change in the 5 years that passed since the fall of Wall Maria and the next time their Titan forms were seen, despite the fact that their human forms did age during this time, which could indicate that the aging of the human form does not affect changes in the Titan form, or that notable changes could be a trait exclusive of their specific forms.

According to Rod Reiss, the power of the Titans rests within a human's spinal fluid, meaning that to gain the Titan's power, it is not necessary to eat the entire human, but rather a Titan can simply bite through the spine and ingest said fluid. Titans serums are, in fact, the spinal fluid of Titans, though study of the serums is difficult due to the serum's rapid rate of evaporation upon contact with air.

Curse of Ymir
Despite the immense power of the Titans, each human which inherits the power is fated with the "Curse of Ymir", which shortens their lifespan to another 13 years once they acquire the power of the Titans. During the last years of their life, the human will have their body weaken until they perish.

Nine Titans
After Ymir Fritz died after using her powers for thirteen years, her powers passed over to nine inheritors. By transferring the power of Titans, those nine Titan lines continued. Through this, there can be a maximum of nine humans with the power of the Titans at any given time. However, after Grisha Yeager ate Frieda Reiss, the line of Founding Titan mixed with the line of Attack Titan. It is unknown that after mixing two lines if is it possible to separate them. Currently, the number of possible existing Titans has been reduced to eight.

List of Lines and Shifters
Founding Titan (始祖の巨人)
 * Ymir Fritz
 * The First King
 * Mr. Reiss
 * Uri Reiss
 * Frieda Reiss - Last descendant of this line. Later mixed with Attack Titan line.

Attack Titan (進撃の巨人)
 * Eren Krueger
 * Grisha Yeager - Mixed with Founding Titan line.
 * Eren Yeager - Current holder. Mixed with Founding Titan line.

Colossus Titan (超大型巨人)
 * Bertolt Hoover
 * Armin Arlert - Current holder.

Female Titan (女型の巨人)
 * Annie Leonhart - Current holder.

Armored Titan (鎧の巨人)
 * Reiner Braun - Current holder.

Beast Titan (獣の巨人)
 * Zeke Yeager - Current holder.

Jaws (顎)
 * Galliard - Current holder.

Cartman (車力)
 * Pieck - Current holder.

Unnamed Titan
 * Marcel
 * Ymir - Current holder.

Trivia

 * Many transformed Titan forms are modeled after mixed martial artists. For instance, the Armored Titan is modeled after  and the Attack Titan is modeled after.
 * Zeke Yeager appears to be the most skilled living Titan, as he possesses the power to mimic human speech in Titan form, climb over the Walls, and create Titans that function at night. Annie Leonhart appears to be the second most skilled living Titan, sporting a variety of learned powers and moves, including selective regeneration, skin hardening, and Titan summoning. However, the holder of the Founding Titan would often be the strongest of all Titans, as noted by Rod Reiss. The least skilled appears to be Eren Yeager, who is still learning how to use his powers, and Armin Arlert, who has yet to experiment with his new Titan form inherited from Bertolt Hoover.
 * While the ability to turn into a Titan is commonly referred to as the "power of the Titans" (巨人の力), this term is also used by the Reiss family to refer to the Coordinate as well.
 * Grisha Yeager consuming Frieda Reiss is the only known case of a Titan shifter eating another Titan shifter. In all other known cases of inheritance of the power of the Titans, the receiver was always a mindless Titan.