In the year 2040, Neuro-synchronization, a technology system that allows humans to manipulate their five senses has become widespread where people can access the internet and enter virtual worlds. Haruyuki "Haru" Arita is a short, fat boy who is constantly bullied, causing him to have low-self esteem. To escape the torment of real life, he logins in the schools virtual world network where he plays squash alone where he always gets the highest score.
One day, Haru attracts the attention of the Student Council Vice-President, Kuroyukihime, who offers him to join a secret program called Brain Burst which allows a person to make time appear to stand still in their surroundings by "accelerating" their brainwaves in the real world. Unfortunately, there is a limit to how many times a person can accelerate which uses Brain Burst points and the primary way to get more points is to fight other Brain Burst users in a virtual reality massive multiplayer online (VRMMO) fighting game and defeat them. However, if a user loses all of his/her points, the Brain Burst program will uninstall itself and the user's ability of Brain Burst will be removed.
Kuroyukihime wants Haru's help as she wishes to reach Level 10 and meet the creator of Brain Burst to learn its true purpose. But in order to do that, she must defeat five other Level 9 users who just so happen to be from "The Six Kings of Pure Color", the leaders of the six most powerful factions in the Brain Burst world. For helping him, Haru agrees to help Kuroyukihime not only to repay her but to overcome his weaknesses.

source:http://en.wikipedia.org/wiki/Accel_World