The Level 6 Shift Plan (絶対能力者進化計画 (レベル6シフトけいかく) Reberu Roku Shifu to Keikaku?, lit. "Absolute Power Evolution Plan") is an experiment specifically created for Accelerator – the strongest level 5 esper in Academy City – to achieve Level 6.
According to Tree Diagram, only Accelerator can achieve Level 6, and by killing Misaka Mikoto – the Railgun – 128 times then Accelerator would be able to achieve level 6. However, since 128 Misaka Mikoto clones could not be prepared with the exact specifications of the current Mikoto, then killing 20,000 level 3 Mikoto clones taken from the Radio Noise project as a subsitute for Mikoto in combat, then Accelerator would achieve similar results. Additionally, the Tree Diagram calculated the number moves Mikoto would make in a battle against Accelerator before he kills her, which is 185 including Accelerator's tendency to play around with enemies.
Level 6 Shift is the focal point of the Sisters Arc, since the reason for the current production of the clones are for Accelerator to kill. Misaka Mikoto is entangled with the experiment in an attempt to save her clones from certain death in the hands of Accelerator. Every attempt by Mikoto to stop the experiments are thwarted with one reason or another, Mikoto concludes that she needs to die in her first move against Accelerator, which would make the calculations of Tree Diagram wrong.
The experiment is stopped by the intervention of Kamijou Touma, who determined that if Accelerator were to be defeated by a level 0 like him, then the assumption of Accelerator being the strongest in Academy City would be incorrect, and the experiment would be stopped since it was based on that assumption of Accelerator being the strongest. Touma faces-off against Accelerator, where he realizes that Accelerator is physically weak and does not know how to streetfight since he defeats his oppopnents in one hit.
Though Touma was able to hit Accelerator several times with his right hand, despite being injured, he later gets put into a disadvantageous situation when Accelerator discovers how to create plasma, and attacking Touma with it from afar. With the help of Mikoto who urges her clones to help protect Touma, he is able to beat Accelerator and end the experiment.
After the experiment that Sisters were later distributed all around the world for readjustments in their bodies, since they were not expected to live long. Though the Level 6 Shift was halted, it was planned by Aleister Crowley – General Superintendent of Academy City – to fail all along since its inception, though he was unaware that it would be Touma who stop it.
The failure of the experiment gave Aleister an excuse to distribute the clones all around the world. This would create an antenna network for a basis of an AIM field umbrella that covers the globe. The resulting network of extended AIM field can then be upgraded into a Artificial Heaven that encompasses the world, creating another plane of existence that would upset the balance of current planes that all Magic is reliant on. Once the balance is broken the rules of Magic would no longer apply and any magicians using magic when the Artificial Heaven is activated would die from a backlash, and all buildings that have magical protection like the Vatican would collapse.
As for Accelerator, Aleister wants him to merge with the Imaginary Number Sector thus allowing him to achieve level 6.