Power of the Titans

"Are you a human being or a Titan?"

- Kitts Woerman to Eren Yeager

Titan Shifters are specific humans in possession of the "Titan's power" (巨人の力), which allows them to transform into Titans. Unlike regular Titans, they are able to control their regular form and retain their human intelligence. It is often noted that Shifters are far more powerful than regular Titans and sometimes display abilities unique only to them.

Description
To transform, they must suffer an injury that draws blood (often self-harm, as shown when Eren Yeager bit his hand to protect Mikasa Ackerman and Armin Arlert, and when Annie Leonhart stabbed her finger with a blade from the inside of her ring) while having a solid goal or belief in mind at the moment of injury. However, being injured by another person is also sufficient, such as when Mikasa seriously wounded Reiner and Bertolt. Once the transformation is initiated, a yellow bolt of lightning appears to strike down the Shifter from the sky, followed by the generation of the Titan body and a release of steam. After transformation, their human bodies appear to be in the Titan's nape of the neck, where they control their Titan bodies. Their human bodies are also merged with the Titan's flesh inside, rendering them immobile. It is also visible that their eyes are connected within the body of the Titan, presumably for optic vision outside the body. An average height among the Titan forms is 15 meters, but this can vary, as shown by the Colossal Titan, the tallest known Shifter, is 60 meters, the Beast Titan is 17 meters, the Female Titan is 14 meters, and Ymir's form is 6-7 meters.

If a Shifter's Titan form is pushed to its limit, its human form will emerge from the nape of its neck in a semi-conscious state. This is demonstrated separately by Eren, Ymir, and Annie when their Titan forms suffer defeat. But if a Shifter's Titan form is not exhausted, then its human form can partially emerge from the Titan form in full consciousness. Annie, Ymir, and even Eren have shown this ability on three separate occasions.

When a Shifter emerges from their Titan body, the area around their eyes is burned from the hot muscle of their Titan forms for a short time after. Every Shifter with a known Titan form has exhibited this at least once, with the exception of Grisha Yeager. The time the burn lasts depends on the Shifter and possibly how long, skilled or how overworked they used their Titan forms, ranging from several minutes to several hours, as shown by how Ymir had the burns over her eyes for almost twelve hours, whereas Reiner and Bertolt only had them for a little less than five hours.

The Titan Shifters also gain the Titan's ability to regenerate, capable of vastly improved healing abilities and regenerating lost limbs even in their human forms. However, regeneration from severe injuries such as lost limbs can strain their powers and prevent them from transforming for a period of time. Both Eren and Ymir were unable to transform while recovering from their injuries, though Ymir is shown to have been able to transform within minutes of recovering. Healing for a Titan Shifter's human form takes much longer than their Titan form, as it took Eren 5 hours to regenerate both of his arms, whereas it would take him minutes to do so in Titan form. The time it takes to regenerate appears to depend on the extent of the injury and how focused a Shifter is on healing that area. The one thing they appear to be unable to regenerate is their head, and the only surefire way to kill them appears to be decapitation, with the exception of devouring them and absorbing their powers.

It is also shown that they are not safe from regular Titans, and will be attacked even while transformed. Both Eren and Ymir were nearly devoured by hordes of Titans while transformed, and Reiner states that traveling while in Titan-occupied territory is dangerous to any of them. During the battle of Trost, it was shown that Titans seem to prefer attacking transformed Shifters. The human soldiers had great difficulty drawing away the Titans, as they were somehow drawn to Eren's Titan form. This is because Titans are regular humans transformed by unknown means and the only way to turn back is by eating a Shifter. Reiner and Bertolt note that it was the same for them.

A notable trait of the three major antagonistic Shifters is their lack of skin, and special abilities unique only to their Titans. For Bertolt's it is steam generation, for Reiner it is his hardened armor, and for Annie, it is a variety of abilities, most notably the ability to harden select areas of her skin and call upon mindless Titans. It is unknown how this relates to Eren and Ymir, who do not share their place of origin or purpose. Ymir displays the ability to partially emerge from the nape of her Titan form, allowing her to interact with others while still transformed. Uri also demonstrated this as well, once being almost completely out of his Titan form with the exception of his right hand. It is unknown whether this is unique to them or a feat that any experienced Shifter can manage over time.

Revelations concerning Ymir's past also suggest several important possibilities concerning the nature of Titans and Titan Shifters, as well as the existence of other Shifters. It is revealed that they do not age while in their Titan form, as Ymir notes she spent at least 60 years in her Titan form but has the appearance of a teenager. Although Ymir lacks complete and clear memory of this period, she recalls enough to describe it as an "endless nightmare." While trapped in her Titan form, she seems to have been a regular Titan that mindlessly devoured humans. Reiner and Bertolt do not treat this as an unusual case, and Bertolt notes that it was the same for them. This leads to the conclusion that the first time of using their power they lack self-determination and have only a decided goal, devour humans. In the case of all the currently known Titan Shifters, excluding Ymir, it appears that there was a Shifter present for them to devour, with only Eren, Ymir, Frieda, and Uri having the Shifter they ate being shown or mentioned.

Experiments performed on Eren suggest that Shifters are resistant, but not immune to the normal absorption that creates mindless Titans if they stay transformed for a long time. After one hour to be transformed, Eren entered in a state of pain and eventually left his Titan body. With the the two subsequent transformations after short rests, the strength and quality of his Titan form degraded more and more, becoming smaller and less controlled each time. On the third transformation, his lower body remained free while his upper body began to merge with his Titan form. It became necessary to cut him loose, removing most of the tissue from the front of his skull in the process. As such, it seems that there is a limitation on how long a Shifter can remain in a transformed state before risking absorption.Similarly, it seems the longer or more often a Titan form is used and how exhausted the human within is, the more difficult the form can be to consciously control. This may cause the Shifter's form to regress to typical Titan behavior and can make them unpredictable if weaponized. The length of being transformed appears to depend on how skilled a Shifter is at controlling their Titan form, as Annie was able to transform twice into a fully formed Titan, in total altogether for almost a day minutes apart, without being absorbed, while Eren nearly lost himself.

Their powers can be transferred to a new host, should they be devoured. This allows an ordinary Titan to become a new Titan Shifter, should they succeed in devouring one—as was the case when Ymir devoured Marcel and regained human form. Hange Zoë theorizes other abilities, such as the Coordinate possessed by Eren, could be transferred to a new host in the same fashion. The Reiss family has done this method for years, by having one Reiss transform into a Titan and devour the previous Coordinate holder, obtaining their powers and the memories of the world.

Grisha Yeager, a Shifter himself, was capable of using a syringe to turn a young Eren into a Titan which in turn devoured most of his body. Similarly, Frieda Reiss became a Titan via syringe in order to consume her uncle to become a Shifter and to obtain the Coordinate ability, as did Uri and Mr. Reiss. The serum induced Titans resemble regular Titans but with a more or less resemblance to the human host, as Eren's normal Titan form resembled him more than his Shifted form with short rugged hair and facial features and Frieda's first transformation led to a skinny, boney female-like Titan with shoulder length light hair. The first transformations are often less shorter than the Shifted forms, but this depends solely on the Shifter, as Ymir's Titan form was 6-7 meters, and was near identical to her Shifter form, whereas Eren's normal Titan was 3-5 meters, while his current Titan form is 15 meters. Rod Reiss revealed that Titan Shifters, who have been given their abilities by having to devour someone, have a chosen Titan Shifter form for them to take. Rod Reiss also reveals that certain serums can create a different type of Titan with different abilities. For instance, Eren consumed a bottle from Rod's bag labeled "Braun" which gave his Titan the power of skin hardening at will.

According to Rod Reiss, a Shifter's power rests in their spinal cord, meaning that to gain the Titan powers, it isn't necessary to eat the entire Shifter, more so just biting through the spine and ingesting their spinal fluid. A serum recovered from Rod Reiss reveals that the Titan serums appear to be spinal fluid. However, it is difficult to study, because once the liquid makes contact with the air, it evaporates.

Notable Titan Shifters
This is a list of known Titan Shifters who's Titan form has yet to be shown in detail:


 * Marcel
 * Uri Reiss
 * Mr. Reiss
 * The First King

Trivia

 * Many Titan Shifters are modeled after wrestlers. For instance, the Armored Titan is modeled after Brock Lesnar and the Rogue Titan is modeled after Yūshin Okami.
 * Annie Leonhart appears to be the most skilled living Titan Shifter, sporting a variety of learned powers and moves. However, the holder of the Coordinate would often be the strongest Shifter, as noted by Rod. The least skilled appears to be Eren, who is still learning how to use his powers.
 * It is possible that like normal Titans, a Shifter's remains evaporate when they perish as there was no trace of Grisha after Keith Shadis found an unconscious Eren after the latter received the Coordinate, even though in Eren's obtained memory, the remains of Grisha's lower body, arm, and clothes were left behind.