Level 5

Level 5 (超能力者(レベル5)) is the highest current Level that espers have achieved in Academy City. Only seven people out of the 1.8 million students in Academy City have been given this rank, which shows how difficult it is to reach.

All the currently known Level 5 espers, have nicknames attributed to them that are related to their powers or are actually their powers. Most egregiously, Accelerator is known only by his nickname.

Characteristics
Level 5s are espers that hold tremendous power, and are far above any other person with powers the same as they are. They are so powerful that their primary powers are banned in the Daihaseisai.

Furthermore, as power development is part of Academy City's curriculum, the strongest of Academy City's espers, such as the level 5s, are most likely also honor students. This is displayed by Mikoto, who has enrolled in Tokiwadai Middle School, and is one of its top students, as well as Accelerator. The Level 5s, apart from their peers, have specialized analysis and research facilities created for them, for example, Accelerator being part of the Special Ability Institute, Dark May Project, and many more.

They 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 a level 5 is dependent on the esper's usefulness in achieving SYSTEM. (This definitely needs to be re-checked/changed the translation for that particular Railgun manga chapter is bad right here. It shouldn't be ranked in order of achieving SYSTEM it should be instead ranked in importance of on-going general research in Academy City only 1 or 2 characters can achieve SYSTEM anyway which makes this completely false)

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 most sane 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 whim, though this may be more related to their background more than anything else.

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.

In addition to this, many of the Level 5s are not on good terms with each other.