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|The War Hammer Titan... It uses hardening to make whatever it needs.|
|— Eren Jaeger assesses the power of the War Hammer Titan|
The War Hammer Titan (戦鎚の巨人 Sentsui no Kyojin?) is one of the Nine Titans that possesses the ability to create any structure out of hardened Titan flesh. Until the Year 854, it was kept within the Tybur family for generations. It is currently in the possession of Eren Jaeger and fused with both the Attack Titan and Founding Titan.
The War Hammer Titan can produce and manipulate structures that are made of hardened Titan flesh. These structures can be weaponized, 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 can also create 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 can also be used to encase the human operator of the War Hammer Titan inside a crystal casing.
Contrary to any other member of the Nine Titans, it is possible for the War Hammer Titan to remove its control center from its nape. Under such circumstances, the body of the Titan will be connected to its human operator by a long cable of flesh, while the human body is encased in hardened crystal and connected with the said cable. Unlike the rest of the Nine Titans, the War Hammer Titan body can emerge from various locations upon transformation because its operator does 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 1,800 years following her death, the War Hammer Titan was held in the possession of one of 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. In the era of the Great Titan War, King Fritz conspired with the Tybur family to instigate the collapse of the Eldian Empire. Using the War Hammer Titan, the Tybur family were able to gain control over seven of the Nine Titans, which they handed over to Marley. The Tybur family were reknowned across the world for driving back the Eldian forces.
After the Great Titan War ended, the War Hammer Titan remained in the possession of the Tybur family, who received honorable status as Marleyan aristocrats. However, 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 secret from all but a select few high-standing individuals in Marley.
After the Marley Mid-East War, Zeke Jaeger 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.
After Eren Jaeger's Attack Titan kills and eats Willy following his declaration of war, Lara Tybur 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, 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. The War Hammer Titan then asks for Eren's final words as she prepares to deliver a killing blow. He calls to Mikasa Ackermann, 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, 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 crossbow to fire a hardened bolt at Eren and Mikasa. Avoiding it, Mikasa reengages the War Hammer Titan, while Eren theorizes that the inheritor was able to survive its nape's destruction due to her body being elsewhere. 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 Lara Tybur 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 Lara. The Jaw Titan ambushes the Attack Titan before it can do so however. While the Attack Titan is distracted, Lara reforms 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. It attempts to devour the War Hammer Titan once again, but 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 Scouts' airship, Eren and Mikasa dismember his Titan. The Attack Titan jams Lara's crystal into Galliard's mouth and forces him to crush it. As the crystal breaks, Eren has Lara's fluids 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.
At roughly the same time Dhalis Zachary is killed by a bomb in his office, Eren uses his War Hammer abilities to escape from his cell. He seals up his exit route with hardened skin to prevent his captors from following him.