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 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. 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 Esther 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.

In the anime, the Coffins often display magic circles when they are utilizing their abilities.

Prototype
The first seen Coffin is the Prototype (プロトタイプ). It is large quadruped mecha, with one large sphere that acts as the eye and is where the corpse of Hitokawa Hasami is located. The mecha has two tentacle-like appendages on of its side. It has powerful legs and is able to leap from a large fissure. In the anime, the sphere is translucent and a mass of tubes arranged in a brain-like shape is visible within.

Using Hasami's ability, Pyrokinesis, it can boost her Level 2 ability to that of a Level 4. In the anime, a magic circle is also visible within the sphere when the Coffin uses the ability.

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 uses a strengthened Stealth Hide ability equivalent of Level 5. It 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.

Background
The Coffins were conceived by neuroscientist Hishigata Mikihiko following his research into which part of the body is the source of an esper's ability. Following numerous dissections and removal of parts from living specimens to see if they still had abilities afterwards, he came to the conclusion that it had something to do with the soul, but also came up with the idea of reinforcing and expanding the body in order to enhance the ability. With the aid of Esther Rosenthal's necromancy, the 23th head of the Rosenthal Family having apparently been tricked into joining his research team as a supervisor but sharing her knowledge regardless without fully grasping the consequences, he made considerable progress and developed the technology which would be used in the Coffins.

At some point during this time, Hishigata allied with DA, providing them with the Coffin technology while using the group and their resources to further his own goals. Esther would turn away from the path after Hishigata Hirumi's death and her attempt to revive her using Taowu, realizing that they should not toy with life and death. While Esther was subsequently held captive, Hishigata continued the development of the Coffins using the techniques he had learned from her, using three of the Evil Spirits of the Numbers (Taotie, Qiong Qi and Hundun) in units,   while also being manipulated by the last one, Taowu, posing as Hirumi.

A couple of days before the events at Heaven Canceller's Hospital, DA operatives murdered Hitokawa Hasami after her failed suicide attempt and installed her corpse in a Prototype Coffin to use her Pyrokinesis.

Necromancer Arc
When confronted by Accelerator after capturing Esther Rosenthal at Heaven Canceller's Hospital, Nishio deployed the Prototype Coffin against him. The Coffin used enhanced Pyrokinesis but was no match for Accelerator, who made short work of it. After the Coffin's destruction, Hitokawa Hasami's corpse fell out of its container in front of Accelerator. Nishio was later terminated for failing his mission and losing the Coffin in the process.

When Accelerator and Esther visited the warehouse where she was once held captive, they found Nishio's corpse as well as the Qiong Qi. After a brief remote discussion, Hishigata moved the Coffin to retreat. Accelerator attempted to prevent it from fleeing but was thwarted by the Qiong Qi's enhanced Psychokinesis, with the Coffin managing to escape.

After the battle with Scavenger, with DA having failed to bring Misaka 10046 to him, Hishigata deployed all the three Coffins which were using the Evil Spirits of the Numbers; Taotie, Qiong Qi and Hundun. After capturing the Sister, Hishigata had the three bring her to him while simultaneously downloading the memories of death from her as they were fleeing from the pursuing Accelerator. Accelerator clashed with the Coffins while pursuing them, and although the Level 5-class abilities posed a bit more of trouble, he eventually overcame them. However, by the time he defeated them, the download had been completed and they had reached their destination.

Buying some time with a ploy, Hishigata installed the formula incorporating the memories of death into the incapacitated Coffins and had them restart, intending for them to delay Accelerator long enough for him to install the formula into 'Hirumi'. The Coffins were ultimately destroyed, but managed to complete their goal.