Level 5

Level 5 is currently the highest esper level to be accomplished in Academy City. Only seven out of the 2.3 million students participating in the Power Curriculum Program have officially achieved this rank, indicating the immense level of difficulty involved in reaching it.

All of the currently known Level 5 espers have been attributed a nickname that is either the name of their esper ability or related to it. Currently, Accelerator is known solely by his nickname.

Promotion to Level 5 is approved by the Academy City Board of Directors.

Characteristics
Level 5s are espers who hold tremendous amounts of supernatural power; their talents far exceed that of other espers, including those with similar capabilities. The abilities of Level 5s are so strong that their primary applications are banned in the Daihaseisai.

Because the Power Curriculum Program is part of Academy City's curriculum, the strongest of its espers are most likely to be honor students. This is exemplified by both Mikoto, who is one of the top students of Tokiwadai Middle School, and Accelerator.

Moreover, Level 5 espers have specialized research facilities that are dedicated to them; for example, Accelerator being part of the Special Ability Institute, Dark May Project, and many more. Misaka Mikoto however is one Level 5 not associated with any research institute, partly due to her own effort and partly due to complementary education of Tokiwadai Middle School, which possesses its own subsidiary facility for Level 5s. Level 5s most likely get paid with the most money amongst their other esper peers as part of the curriculum's payment program for the espers as being part of the experiment.

Also, it seems that Academy City views Level 5 Espers (and others in general) as a threat, due to the fact that their developing minds can make them act based on emotions rather than logic. In order to rest easy, they have created Rensa, a cyborg that can use the abilities of the #1 up to #6 in order to deal with them in the case they decide to go against the city, and she supposedly can defeat all seven of them.

The ranking of the Level 5s is dependent on the worth of their abilities to the ongoing researches rather than based on the relative strength of their power. Their counterparts are the Saints from the magic side.

Personality
A particular object of notability of all the Level 5 Espers is a recurring instance of mental instability, be it comedic or serious. Mikoto, the first Level 5 seen in the series, has a comedic obsession with defeating Kamijou Touma, although she has been referred to as the sanest one out of all the Level 5s. Sogiita Gunha believes himself to be an ally of justice and purposely acts in accordance of superheroes in fiction. Accelerator, Kakine Teitoku, Mugino Shizuri, and Shokuhou Misaki all demonstrate more sociopathic or psychopathic tendencies with the willingness to hurt people on a whim, though this may be more related to their background more than anything else. However, both Accelerator and Mugino have become less violent lately because they feel guilty about all the harm they've done. Misaki has also demonstrated that she does care about her friends and is willing to go out of her way to save them.

Due to this, only Mikoto is the one apparently competent enough to be used as a marketing mascot or demonstrator for Academy City. Even then, it is not unheard of for any of the Level 5s to be requested for demonstration.

That said, the essay The Wall Between Level 3 and Level 4 from Toaru Majutsu no Index no Subete seems to reject this premise, stating that gaining high level powers like Accelerator and Mikoto did is the result of having strong minds and firm ideologies and principles.

In addition to this, many of the Level 5s are not on good terms with each other, although they would still sometimes form alliances if the situation called for it.

Trivia

 * When discussing the existence of Anna Sprengel with Kamijou Touma and Accelerator, Aleister Crowley uses the term "#0 Level 5" as comparison, showing the mystique and persuasive ability of "a missing superior rank". As it was only an example, it is unknown if the 0th Level 5 exists even after Anna Sprengel was proven to be real.
 * At the time of this analogy, the existence of the Beginning Child, the first modern esper developed before the present-day ranking system and speculated to qualify for Level 5 under the current scale, had not been revealed.