|It controls Titan hardening to create weapons, or anything it needs, from underground.|
|— Eren Yeager assesses the power of the War Hammer Titan|
The War Hammer Titan could produce and manipulate structures that were made of hardened Titan flesh. These structures could be weaponized—for example, forming pikes large enough to impale and lift a Titan, flooding areas with protrusions such as spikes, and manifesting the Titan's signature war hammer. This ability could also create serrated and bladed weapons such as a sickle or even flexible weaponry components, such as the string of a crossbow or the whips of a cat-o'-nine-tails, making this a particularly unique brand of hardening. Much like the Female Titan, this hardening could also be used to encase the human operator of the War Hammer Titan inside a crystal casing. Unlike the Female Titan, however, the human retains consciousness while encased inside the crystal. While durable, this crystal could be damaged when struck or crushed by a more resilient structure; however, the only structures that were proven capable of such a feat were the Jaw Titan's claws and teeth.
It was stated by Theo Magath that while they are certainly a powerful asset, the War Hammer Titan's structural hardening abilities were to be used in moderation; otherwise, constant usage in a short amount of time could quickly deplete the user of stamina.
Contrary to any other member of the Nine Titans, it was possible for the War Hammer Titan to remove its control center from the nape. Under such circumstances, the body of the Titan would be connected to its human operator by a long cable of flesh, while the human body was encased in a hardened crystal and connected with the said cable. If the cable was severed, the War Hammer Titan's body would be deactivated, although a new Titan body could still be made. Unlike the rest of the Nine Titans, the War Hammer Titan body could emerge from various locations upon transformation because its operator did not need to be inside of its nape.
The War Hammer Titan, like all the Nine Titans, was brought into the world after the death of Ymir Fritz. In the 1,700 years following her death, the War Hammer Titan was held in the possession of one or several of the warring Eldian houses subservient to the Founding Titan. After these seventeen centuries, when King Karl Fritz abandoned the conflicts of Eldia and relocated to Paradis Island, the War Hammer Titan had come into the possession of the Tybur family. At some point, the uprising peoples of Marley took part in the Great Titan War; and the Tybur family were the first Eldians to come to their aid in the early days of the war.
After the Great Titan War ended, the War Hammer Titan remained in the possession of the Tybur family, who swore to defend the new nation of Marley as honorary Marleyan aristocrats. However, despite this vow, the War Hammer Titan remained unused in battle throughout the next century. For reasons of security, the identity of the War Hammer Titan within the Tybur family was kept a closely guarded secret from all but a select few high-standing individuals in Marley.
After the Marley Mid-East War, Zeke Yeager develops some concerns towards the fate of the Eldian race, given the world's rising technological advantage over the Titans and, by extension, over Marley. In order to improve the reputation of the Eldians in the eyes of other nations, Zeke convinces the Tybur family to support the next attack on Paradis Island with the power of their War Hammer Titan.
Shortly afterward, when the Tybur family arrives in Liberio, Willy Tybur converses with Commander Theo Magath concerning the state of their nation. When asked whether Magath can determine which Tybur holds the War Hammer Titan, Magath admits he is at a loss. However, Magath later notes that Willy speaks of the history of his family and nation as if he had witnessed it firsthand. Willy admits that he has indeed seen history firsthand due to the memories that the War Hammer Titan has carried throughout its inheritors within the Tybur family throughout the past century.
After Eren Yeager's Attack Titan kills and eats Willy following his declaration of war, his younger sister transforms into the War Hammer Titan. The Attack Titan immediately interrupts the War Hammer Titan's transformation by unleashing numerous punches on its upper body. Eventually, it recovers and generates spikes in the ground that immobilize the Attack Titan. The War Hammer Titan regenerates its upper body, completes the transformation, and creates an enormous war hammer for itself to use. Trapped and being shot at by anti-Titan artillery, the Attack Titan is unable to successfully block the incoming swing of the War Hammer Titan's hammer and is swiftly beheaded. After decapitating the Attack Titan, the War Hammer Titan prepares to deliver a killing blow as Eren emerges from its neck, then asks for his final words. Eren calls to Mikasa Ackerman, who suddenly appears from behind and catches the War Hammer by surprise. Despite trying to stop her, the War Hammer Titan is barraged with Thunder Spears launched by Mikasa, most of which fly into the Titan's nape and set off a massive explosion that sends it crashing to the ground.
Even with the total destruction of its nape, the War Hammer Titan stands back up and forms a smaller pike, launching it via crossbow at Eren and Mikasa. Avoiding it, Mikasa reengages the War Hammer Titan, while Eren theorizes that the inheritor must not be located in the nape; thus, the user of the War Hammer Titan was able to easily survive the attack. He begins to track where the inheritor could be hiding and eventually notices a long cable stemming from the Titan's left heel. Following it and transforming into the Attack Titan once more, Eren finds the younger sister of Willy underground, encased within a crystal and attached to the end of the cable.
The Attack Titan proceeds to sever the cable, rendering the War Hammer Titan immobile, and then attempts to eat the inheritor. The Jaw Titan ambushes the Attack Titan however, giving the younger sister of Willy time to reform the cable and generate an incomplete War Hammer Titan body, that traps the Attack Titan in a tree-like structure of Titan hardening.
However, the Attack Titan instinctively hardens its arm to protect its nape from the attack. The Attack Titan attempts to devour the War Hammer Titan once again, but it fails due to the crystal barrier shielding the operator. Realizing the War Hammer Titan is out of power, Eren frees himself from the nape of the Attack Titan, and transforms once more.
After Eren picks up the crystal in his new body, the Jaw Titan rushes to attack him, unleashing a flurry of attacks with its sharp claws and inadvertently leaving a deep scratch on the crystal when Eren raises it to protect himself. Later, when Galliard tries to attack the Survey Corps' airship, Eren and Mikasa dismember his Titan. The Attack Titan jams the War Hammer crystal into Galliard's mouth and forces him to crush it. As the crystal breaks, Eren allows the younger Sister of Willy's fluids to drain into his Titan's mouth, giving himself the power of the War Hammer Titan.
While he is imprisoned, Eren explains to Hange that he ate the War Hammer Titan and is fully capable of using that Titan's abilities to leave his prison whenever he wants, no matter how tough and deep the underground cell is. He later does so and, to prevent being followed by the military, uses the War Hammer Titan's abilities to seal his escape route.
During Marley's attack on Shiganshina District, Eren uses the War Hammer Titan's hardening abilities to great effect; after generating spikes from his back to prevent the Jaw Titan from ambushing him, Eren later generates numerous rows of spikes from the ground to incapacitate both the Jaw and Armored Titans.
- On February 8th, 2018, Hajime Isayama revealed on his blog a rough draft of the War Hammer Titan's head and neck.