OverBlade

OverBlade (オーバーブレード, Obaburedo) is an extremely powerful and lethal computer program which was developed by Suoh Agare as his ultimate weapon in ensuring his eternal dominion over Sword Art Online. It is considered the one true "class" in SAO, and can only be obtained under the rarest and most obscure of circumstances, such that it is almost completely and utterly impossible for anyone in the game to actually become an OverBlade without knowing the exact methods on how to achieve it. There are only a handful of players in SAO who ever managed to obtain the status of OverBlade, the strongest and most notorious of which being Genato and Agares.

Techniques
A term coined by the designer of the skill, Agare Suoh put together the words "Overlord" and "Blade" in order to outline precisely how powerful nd mighty one would become should they ever obtain the power that is the OverBlade class in SAO. When a player is promoted to the status of OverBlade, they immediately obtain unlimited to access to every single ability, item, skill, and object in SAO, including all Sword Skills, Extra Skills, Unique Skills and Outside System Skills, effectively transforming the player into the single most powerful being in Sword Art Online. In this way, the user obtains the ability to perform a nearly unlimited roster of devastating sword skills and techniques, some of which only the OverBlade status is capable of executing.

Skill Description
The OverBlade was designed by Suoh Agare personally after discovering Kayaba Akihiko's sinister plans and devices for SAO and the NerveGear. Rather than exposing him before SAO could take place, Agares concocted an intricate plan of even more sinister proportions, and began working in secrecy on a new gameplay feature that only he would know about. This gameplay feature was designed to be the downfall of Kayaba Akihiko, which he would use to defeat him at the 100th floor of castle aincrad and usurp his place as the most dominant being in sword art online. As a means to an end, Agares loaded every possible exploit into the skill and implanted it in secrecy into the system of SAO, flawlessly putting his greatest weapon into the game in a way that it could never be detected or patched.