Story related and cannot be missed.
The Berserk Hunter is the second out of three Hunter bosses in RoE.
This boss is more aggressive than the previous boss and has two attacks. One is a leap like melee attack; the other is once again launching fireballs. When the battle starts, use the Bloodstone and continue to fire the Super Shotgun into his heart. It should be noted that he can only be harmed while his chest is open and his heart is exposed and glowing.
Here is a video of the battle by Urbanator123: