Berserker's identity is Tamamo Cat (タマモキャット, Tamamo Kyatto?), one of the Tamamo Nine. After Tamamo-no-Mae underwent a millenium of training and attained divinity, she cuts off her other 8 tails when she returns to her one-tailed form. Each of her tails is left a portion of her divinity and becomes a heroic spirit.
She is the crystallization of Tamamo's more pure and sincere aspects.
Berserker's Noble Phantasm is Bright Sunlit Nap.