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 Si-Xiong (四凶) banished by in the book, the fourth being the Taowu.

Principles
The Coffins are a product of Hishigata Mikihiko's research into where esper abilities originate from within the human body and a reverse application of an effect observed during the course of this research. During the experiments, it was observed that when the test subject's body was reduced, their ability's output was also reduced. Conversely, Hishigata realized that abilities could be strengthened by making the body bigger. In order to achieve this, the subject would be connected to a machine and the brain made to think that the whole thing, both the original body and the machine reinforcing it, was its "body".

While it was indeed possible to strengthen esper abilities by enhancing the physical body in this manner, there were difficulties in having the brain recognize and process having the machines as part of the "body",   and Hishigata could only get the method to work with the specially treated dead brains of esper corpses reanimated using Rosenthal-style Necromancy. As such, the Coffins utilize an unusual combination of technology, esper abilities and magic.

In addition to Hishigata's application of his research coupled with the necromantic techniques and charms he obtained from Esther Rosenthal, Coffins were also produced using resources (technology, corpses and funds) supplied by DA and their backers. DA expected them to be used as weapons to enforce their 'justice',     though Hishigata was merely using their resources to further his research towards Level 6, pursuing the perfect brain and body. In turn, the Rosenthal ancestor Isaac, imprinted onto Taowu and posing as the late Hishigata Hirumi, was also using this research to acquire the perfect vessel and perfect soul for the perfect golem sought by the family.

The Coffins have the basic framework of a large mechanical weapon, equipped with sensors, propulsion systems and some conventional armaments. Contained within a spherical section of the Coffin is a corpse (hence the name),  which has been reactivated using the Rosenthal-style method of inserting an artificial soul stored in a charm into the body to reanimate it. The dead body is connected to the Coffin and the dead brain has been made to recognize the machine as part of the body, enabling the Coffin to make use of the deceased esper's ability at an increased level due to the larger body supporting it. Both the machine and the artificial soul are meant to follow commands, and the Coffins follow the commands of their controllers, such as Hishigata or the DA operatives using the weapons, but they have a degree of autonomy in carrying them out.

All of the known Coffins have displayed an ability output roughly two levels greater than their occupant's normal level. The Prototype, using a low-level spiritual charm, boosted Hitokawa Hasami's Level 2 Pyrokinesis to Level 4,  while the Coffins using the Evil Spirits of the Numbers; Qiong Qi, Taotie and Hundun, had Level 3 occupants and exhibited Level 5-class abilities. Additionally, the latter three's capabilities could be enhanced further by installing the special formula derived from the Sisters' 10031 memories of death, which was ultimately meant to artificially shift Taowu to Keter.

In the anime, the Coffins often display magic circles when they are utilizing their abilities, reflecting the use of Rosenthal-style magic in their operation.

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 Coffin which uses one of the Evil Spirits of the Numbers bearing the same name and Psychokinesis strengthened to Level 5-class.

It has a much more streamlined (particularly in the anime) and animal-like appearance than the more machine-shaped Prototype, with a central spherical body with tubes connecting from it to a pointed 'head', two long forelimbs with rear-mounted bars (manga) or retractable 'feathers' (anime), and a rear section with two hindlimbs and a 'tail'. In the manga, there is a curved band behind the central region and around the shoulder joints,     while in the anime, there is a hump on the rear of the spherical section. Most of Qiong Qi has a turquoise blue coating, with a red symbol from the charm glowing on its 'collar'.

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 Coffin which uses one of the Evil Spirits of the Numbers bearing the same name and a teleportation ability strengthened to Level 5-class. It is much more blocky in appearance than the other Coffins,  with a central rectangular section and four similarly shaped pods, two attached either side of the central section with one ahead of the other, each with a retractable leg on their underside. A horizontal bar is mounted on top of the rear end of the central section and a pod is fitted on each end of this bar, with a large gun barrel extending from the front of the right one. A movable cable extending out of a hole on the top-middle of the central section connects through a spherical section and then to the unit's 'head'. The central section and rear bar are colored black while the pods and 'head' are coated dark purple.

Taotie has rocket thrusters on its rear bar and below the inner pods for flight purposes,  though when stationary it tends to remain on the surface. It is armed with two retractable machine guns on top of its central section, a large supply of missiles launched from the outer left pod on its rear bar,  and a high muzzle velocity cannon (manga) or gatling gun (anime), mounted on the outer right pod with a long barrel. It also has anchors which are deployed when it uses the high muzzle velocity cannon.

Taotie utilizes a teleportation ability, known as Replace in the anime, which allows it to remotely switch the positions of targets, including itself. In life, the sample esper's ability could only allow them to trade places with their favorite stuffed animal. In the case of the Taotie, it can swap the positions of marked targets in sight, which the brain has been hypnotized into thinking are the stuffed animal,  with itself or with other marked targets within its field of vision. These include its missiles and other Coffins.

After having the memory formula installed, Taotie's ability was enhanced further. Whereas before it could only teleport marked targets, now anything could be forced into the stuffed animal role and targeted for teleportation. In addition, the formula allowed Taotie to use its ability outside of its normal range by visually linking with Qiong Qi, allowing Taotie to teleport targets seen by the cameras connected to Qiong Qi and swap them with targets in Taotie's own field of vision. Taotie's enhanced form of teleportation in conjunction with the Psychokinesis-wielding Qiong Qi, referred to as Asport (遠隔射出 (アスポーツ)) by Accelerator, was capable of teleporting Qiong Qi in from afar and even Accelerator himself, whose redirection normally interferes with teleportation abilities, without his consent.

Hundun
Hundun (混沌) is a Coffin which uses one of the Evil Spirits of the Numbers bearing the same name and a concealment ability strengthened to Level 5-class. Mostly covered in brown coating, it has a central spherical section with holes on six sides, with a spine-like section extending down from the bottom one to a tripod-like base with three 'legs' connected with cables. A cable from the sphere's top hole connects to an elongated 'head', while cables from the four side holes each connected to a large shield.

Hundun is equipped with several rocket boosters, with two on each of its four shields, for flight purposes. It also has several tendril-like appendages, with pronged (manga) or spiked (anime) ends, which can be wrap around and grab targets. They could also attach to and fit a helmet (manga) or connectors (anime) to Misaka 10046 in order to extract the memory data to transmit to Hishigata's computer.

Hundun utilizes Stealth Hide (ステルスハイド), a concealment ability which dulls the senses of humans around it. In its strengthened form, it inhibits any recognition of the unit. Although this ability cloaks Hundun from view, it doesn't erase its physical presence, so signs of motion and disturbances in air currents can be used to calculate its location. Damage to the unit can also disable the cloak. When engaging and disengaging its Stealth Hide, blue hexagons briefly appear around the Hundun.

L-type Lab Equipment
In the anime, there was a predecessor to the Coffins, in the form of a machine referred to as the L-type Lab Equipment (硏究機材Lタイプ). The machine had four legs and a suspended body, with test subjects stored in a red container on one of the body's sides.

The machine acted as life support during experiments involving shutting down organs to determine if it affected the test subject's ability. During the course of this research, it was observed that the larger the life support equipment serving as the subject's body, the higher the ability's output became. However, increasing size also acted to destroy the subject's sense of self, and many of them ended up in a broken state.

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.

Following the battle with Scavenger, with DA having failed to bring Misaka 10046 to him, Hishigata deployed all of 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 and rescued the Sister. However, by the time he did so, 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.