Sentinels

Sentinels are giant robots created to fight against the Deimos invasion. They can only be piloted by Compatibles.

History
The Sentinels were inspired by the Type-98 Biped, which fought the Kaijus during the final battle in Sector 4 one loop ago, but ultimately failed to stop them. Tetsuya Ida, who personally piloted one such weapons during the final battle, noted their lack of arms and commented that they were completely defenseless against Kaijus once they closed in.

Just before the destruction and reset of the world, Ida was sent to Sector 0 thanks to the sacrifice of Chihiro Morimura from two loops ago. He appeared on Sumire Bridge in Sector 1, 2089; right next to a new iteration of Chihiro Morimura, who only had her memories from two loops ago. Ida convinced Morimura to join her in trying to stop the Kaijus.

In the eleven years that followed, Ida developed the first generation of Sentinels. To address the weakness of the Type-98, they had a heavy emphasis on melee combat capabilities. However, the earliest Sentinels refused to respond due to influence from Deimos code, leading Morimura to the conclusion that they have to be directly controlled by a Compatible.

A total of twelve Gen 1 Sentinels were manufactured. Originally, they were all designed to be remote controlled. However, due to low efficiency and responsiveness caused by Deimos interference, No. 10 and No. 11 were refitted into piloted models. Tsukasa Okino also installed additional equipment, including EMP emitters and anti-air flares, onto the Gen 1 Sentinels.

Eventually, Tsukasa Okino designed three more generations of Sentinels: Generation 2, which featured both close range and long range weapons; Generation 3, which specializes in long range combat; and Generation 4, the most mobile Sentinels with flight capabilities. However, Generation 4 Sentinels were not produced by the time the battle for Sector 2 took place.

Following the battle for Sector 2, 426 acquired the Deimos key from Natsuno Minami and used it to send orders to the automated factories, creating the Generation 4 Sentinels.

Technical information
Similar to their predecessor, the Type-98, all Sentinels are equipped with a transmission device, allowing them to move between sectors. This also enables Sentinels to be teleported to a pilot's location.

Sentinels from No.12 onward were all designed to be piloted. Sentinels do not have a cockpit hatch, and pilots enter and leave the Sentinel through teleportation. Inside a Sentinel's cockpit, the pilot loses all of their clothes. Though some accessories, such as glasses and bandages, appear to remain.

As Okino explained, however, the Sentinels did not actually have a cockpit, as simply throwing a punch in a Sentinel would cause the pilot to experience recoil comparable to a train crash. Instead, the Sentinels borrowed some of the Universal Control's systems. When a pilot "enters" a Sentinel, they are actually teleported to the growth pod in which their real body resides.

Since they were never intended to act as cockpits, the growth pods lacked any sort of controls for the Sentinels. Instead, the Sentinels were piloted by thought. Through the nanomachines in the pilot's brain, the Sentinel transmitted information directly into the pilot's mind, in the pilot's own voice. The Sentinel also projected a weapon display into the pilot's eyes.

Operating a Sentinel places a heavy strain on the pilot's brain. As such, it has a limited operational time. Pilots require a rest period after consecutive battles. If a pilot continues to operate a Sentinel past its operational limt, their brain nanomachines may begin to peel off, causing them to suffer amnesia at best and become vegetative at worst.

Sentinels have a self-repair function, which can either be manually activated or automatically activated when the Sentinel either takes too much damage or reaches its operational limit. When the self-repair is in progress, the Sentinel teleports away, leaving the pilot unprotected on the battlefield until the repair is complete. The automatic self-repair can be overriden by the pilot in an emergency, though doing so risks the pilot's life as the Sentinel's life support system is pushed beyond its limit.