In Mikasa Ackermann and best friend Armin Arlelt, the 104th Cader Corps, which gives way to Eren’s discovery of unlocking the power of a Titan itself.
Humans residing within the three Walls on Paradis Island were taught that the first Titans appeared 107 years prior to the year 850, after which, they began exterminating humanity to the point of near-extinction. While the regenerative abilities of a Titan vary in extent, it is known that each one is able to regenerate lost body parts within a matter of minutes. One of the sure-fire ways to ‘kill’ a Titan is to slice through the nape with two blades, with an exact measurement of 1 meter and 10 centimeters. As the nape of a Titan is akin to Achilles’ heel, striking the area results in death before its regenerative abilities find a way to, in a sense, reboot.
This is deemed possible, as cutting the nape of a Titan cuts off the absorbed human brain and nervous system within the giant, in turn, killing the person and the Titan instantly, since it is piloted by the unconscious human inside it. It is interesting to note that while only the spine of a human is absorbed in Pure Titans, in the infinitely-more powerful Nine Titans, the entire human body is absorbed. Hence, without a functioning nervous system to control it, the Titan ‘dies’, with some corpses rapidly evaporating to skeletal remains, which then proceed to turn to dust. This makes sense as the nape of the neck is where the brain roots connect with the spinal columns, and once this connection is severed, the Titan loses with the rest of its body, losing its regenerative abilities in the process.
Further, it has been theorized that Titans operate by heating gas and expanding a carbon-fiber-esque polymer, which forms their giant, muscular bodies. Despite possessing superhuman strength that can break human bones on , these fibers are weak in of shear strength, which explains why their limbs can be severed easily with swords. Also, per the Japanese light novel Attack on Titan: Before the Fall, which serves as a prequel to the manga’s events, the humans figured out the Titans’ weakness 30 years after the wall was built, when a Survey Corps member named Solm Hume sacrificed himself by blowing himself up atop a Titan’s neck.
After much trial and error, weapon-smith and creator of the vertical maneuvering equipment, Angel Aaltonen, figures out that it is the nape in particular that kills a Titan, leading him to detonate gas canisters in the area, leading to the death of the Titan. More details about the history of the Titans and Titan Shifters might be revealed in the near future, allowing fans to better understand their motivations and the fate of characters such as Eren or Reiner, along with an inevitable, all-out war between Eldia and Marley. Whether the Titans can be vanquished once and for all, remains to be seen in the currently-unfolding Attack on Titan season 4, which is deemed to be the final season of the popular anime adaptation.
