SYSTEM

SYSTEM (システム) is the main goal of Academy City's research, defined as "Those who are not deities that reach the sense of the heavens" (神ならぬ身にて天上の意思に辿り着くもの), it is the core of Aleister Crowley's plan, as well as many research organizations in the city.

Level 6 is used as an interchangeable term for it, which can refer to an esper that has surpassed Level 5 and has reached SYSTEM or for SYSTEM itself.

Principle and Concept
The concept has been referred to since the beginning of the series with Misaka Mikoto referring to the struggle of the city trying to find a body that exceeds humans and can do God's calculations. SYSTEM is first referred to in name by Tsukuyomi Komoe while explaining what esper development is to Index and Himegami Aisa.

Both Tsukuyomi Komoe and Kihara Gensei, state that the goal of SYSTEM is to understand the will of the heavens, and to achieve it is to find a human that surpasses humanity. The city is dedicated into finding this, the most logical way is to have a Level 5 actually achieve Level 6, most specifically Accelerator. However, there are probably other methods of achieving it, such as with the case of Haruue Erii and the Crystallized Esper Essence.

According to Mugino Shizuri, Level 5 rankings are based on the importance of the Level 5 on the research of achieving SYSTEM.

The apparent reason why SYSTEM is trying to be achieved, is to gain the knowledge regarding the truth of the world, something that many a man of countless immemorial eons have tried to gain, even on the magic side.

Experiment
As stated the purpose of Academy City was to create a Level 6, and most likely several experiments have been undergone to achieve it.

One of the most notable experiment in achieving a Level 6 was the Level 6 Shift, an experiment supported by Tree Diagram and is centered around Accelerator. The goal of the project was for Accelerator to kill specially prepared 20,000 Misaka Mikoto clones, in order to achieve SYSTEM. The plan fails as Kamijou Touma intervenes with the 10032nd experiment and defeating Accelerator.

The experiment was later revealed to have been planned to fail even without Touma's intervention, as it gave a Aleister Crowley an excuse to distribute the clones all over the world for "readjustments", although in truth, it was created in order for the clones to cover the globe with AIM which are dispersed by espers, namely the clones. Moreover, it is to create an Imaginary Number District-like realm, an Artificial Heaven into the world, which when activated by Aleister Crowley, completely disrupts a magician's ability to use magic, and severely injuring them, although it is unknown what the true extent of a perfected realm's effects on magicians is.

Qabbalah
After Komoe explains SYSTEM to Index, she shuddered in fright, as the concept of SYSTEM sounds close to the Qabbalah of the Magic side, where the heavens are not described on the Tree of Life – Sephiroth – though other areas like humans and angels are clearly stated. Wherein the positions of humans, angels and god are divided into 10 levels, and upon that tree, the position of God could not be found. As such, humans could not understand the territory of God.

According to the narrative, there was stated that a religious system to achieve understanding of God's territory. The concept is called Gnosticism, which stated if humans can't understand then all they have to do is obtain a body that's beyond humanity. They claimed that humans are but immature gods that can reach ascension and God's power with enough training, which even the Apostle John sees as blasphemous.

Alchemy
Himegami Aisa thought of Aureolus Izzard's "Ars Magna" - whose principle behind it is "to purify the murky, lead-like soul of a human into a pure golden soul of an angel". It also occurred to her that it's strange how Academy City, a force that's completely opposite to religion arrived at the same answer. It could be that whatever path humans take they would arrive at the same answer, or maybe there's something else behind all this.