Accel World, Vol. 3: The Twilight Marauder - light novel

Prepare for a full dive!
His life completely transformed since meeting Kuroyukihime, the most beautiful girl in school, Haruyuki has grown up into a magnificent knight, fat and bullied though he might be. As the season turns to spring, a strange new student appears before Haruyuki and his friends, now in eighth grade. This mysterious seventh-grader has mastered the art of using Brain Burst in everyday life, despite being curiously absent from the Duel-matching list.
With Kuroyukihime away on a field trip for the ninth grade class, this new member of the student body, in the guise of a warped duel avatar called Dusk Taker, steals "something precious" from Haruyuki with overwhelming force. Cast once again to the bottom rungs of the school-hierarchy ladder, Haruyuki is driven into a corner, and his only course of action is--?!