It is a large yellow-painted mechanical unit, with two large legs to support it's weight. It has at least 4 arms that has clamps on it, two of which are attached to a large bulky attachment to the torso of the unit, which has exhaust ports at the top, implying it is where the engine of the units is located. The cockpit can be found in the middle of the torso, which has several interfaces for piloting the unit.
It has the MAR initials painted on it, indicating it's use and ownership by MAR.
- Main article: Poltergeist Arc
The mechanical unit makes it's only appearance in Toaru Kagaku no Railgun being piloted by Therestina Kihara Lifeline during the in attempt to stop Kiyama Harumi, Misaka Mikoto, Uiharu Kazari and Saten Ruiko from reaching the Child Error's that she kidnapped. Despite its overwhelming size, it had no trouble of catching up to Harumi's car and gave them much trouble before it is later destroyed by Mikoto's upgraded Railgun.
The unit has no weapons, but with its large size can practically overpower most opponents it may encounter. It also seems to be capable of defending itself against electric shocks.
Its most notable attributes are the clamps that are attached to its four arms, which can be used for smashing and grasping of things, most uniquely it can be used to fire it as projectiles, though once fired the clamps can no longer be usable and cannot be returned to the arm. At which point the pilot can simply eject the arm from the unit. Finally, the mechanical unit makes use of rollers under its feet, which makes it more mobile.
Since it is used by MAR and due to being colored yellow (for high visibility), and due its large size and durability, it can be inferred that the mechanical unit is used for heavy-duty rescue operations.
- The large mechanical has similar characteristics to the Knightmare Frame of Code Geass fame, especially the clamps that are similar to the weapons of the typical Knightmare Frame, as well as the rollers that are used for movement.