Battle fury, also translated as battle rage. A berserker special status. It is also linked to battle fatigue.
The Berserk need to reach a certain amount/intensity of fighting rage.
The berserker get a bonus in combat stat, and also access to special skill like Raging sword. After the fight, he will be more vulnerable.
Battle Fatigue/Stat Loss: After a berserker fight for an overly extended length of time (seemingly determined by the intensity of the fight), he will will suffer a backlash (stat losses and damage) that are proportional to the Fury previously unleashed.