Berserker is a warrior from the Warring States Period, the son of Mori Yoshinari from the Oda clan, and the elder brother of the famous Mori Naritoshi (Ranmaru) who served as Nobunaga's attendant. A brave warrior who's earned the nickname "Oni Musashi" for his many military exploits and the spearmanship that was taught to him by his father who was famed as "Sanza the Attacker."

(Source: Type-Moon Wiki)