Coffin

Coffins (棺桶) refer to large mobile weapons that are controlled by the corpses inside, specifically that of an esper. Coffins are able to boost the powers of the espers inside them and are able to use them to great effect.

First introduced in Toaru Kagaku no Accelerator, they are manufactured and used by the DA to cleanse Academy City of "evil".

Etymology
Qiong Qi, Hundun, and Taotie are mythical Chinese creatures as mentioned in the . They are three of the Four Fiends in the book, the fourth being the Taowu.

Principles
The Coffins uses "evil spirits" of the numbers to allow it to function. It is currently unknown what these are. These are actually artificial souls created by the Rosenthal Family to allow them to reanimate corpses.

Coffins were brought about Hishigata's research in trying to find the origin of esper powers in the body, eventually concluding that it comes from the soul. His research showed him that he could strengthen esper abilities by enhancing the body, and with Estelle Rosenthal's help, used the corpses of espers as basis for this. He made it so that the "enhancements" of the body aka the mecha that would become connected to the corpse of is merely a part of the esper's power. And with the possession of the artificial souls in the corpses allowed Hishigata and anyone who is authorized to do so complete command of the Coffin. Indeed, the abilities of the esper dramatically increase enough to be even categorized as a Level 5 ability.

Coffins are however just of Hishigata's research in acquiring the perfect brain and the perfect body to create the perfect esper, a Level 6. In turn, the Rosenthal Family ancestor Isaac, whose soul was imprinted into the Taowu and later possessed the body of Hishigata's sister, Hirumi, is also using Coffins in his research in acquiring the perfect vessel and the perfect soul to create the perfect golem: God. Both of whom used DA and other organizations to fund  and it is likely the use of Coffins to DA was part of this.

Prototype
The first seen Coffin is the Prototype. It is large quadruped mecha, with one large sphere that acts as the eye and is where the corpse of Hitokawa Hasami. The mecha has two tentacle-like appendages on of its side. It has powerful legs and is able to leap from a large fissure.

Using Hasami's ability, Pyrokinesis, it can boost her Level 2 ability to that of a Level 4. As Hasami would late be found with a magic circle written on parchment stuffed inside her mouth, and later Estelle making use of the same magic circle to repossess Hasami, it is likely the Coffin or the spirit possessing Hasami inside the Coffin was Huotou.

Qiong Qi
The Qiong Qi (窮奇) is a large Coffin that uses a strengthened Psychokinesis ability equivalent of a Level 5. Unlike the more machine-like Prototype, the Qiong Qi is much more streamlined and animal-like in appearance. It has a head where its eyes are located, four legs, and two arm-like projections on its sides.

It is very powerful, able to dissipate Accelerator's wind attack. It is used to kill Nishio, mutilating his body and even melting his flesh. Similarly to the Prototype, it can make powerful leaps up to the sky. The machine is capable of injuring Accelerator even with Redirection, something he compares to that of Kamijou Touma.

Taotie
Taotie (饕餮) is a large Coffin that is much more rectangular in appearance than the other Coffins. It can fire both missiles and has two machine guns. It can leap high, though it has been shown to stay more on the ground. It has the Teleport power, allowing it to teleport objects, like its missiles, without touching them. It is later destroyed by Accelerator.

After acquiring the formula that included the data on the 10,000 deaths experienced by the Sisters, Taotie's teleportation power is increased. In conjunction with Qiong Qi's cameras, it allows Taotie to teleport objects without touching or being physically present or near its target. This ability known as Asport is even strong enough to prevent Accelerator from redirecting it, teleporting him without his consent.

Hundun
Hundun (混沌) is a Coffin that is much taller than both Qiong Qi, and appears bipedal. It has several rockets that allow it to fly into the air. It also has several tendril-like appendages allowing it to grab objects. It was these that allowed Hundun to put a helmet on Misaka 10046, to allow data regarding her to be transferred to Hishigata's computer.