Nine Lives

Nine Lives is the most trusted Noble Phantasm of the Heroic Spirit Hercules. It is the bow and arrows used to exterminate the hydra and its nine heads that would grow back no matter how many times you would cut them down; he later ports that attack to be able to use it with weapons such as a giant sword.

Hercules could make a splendid use of that attack if his class was Saber. That secret skill was used with the projected axe-sword to kill the blackened Berserker.

Source: Fate/Side Material encyclopedia entry (p.68)

Nine Lives is a skill that can adapt itself depending on the circumstance and target, and look different; that makes it an all-purpose Noble Phantasm, so much that you could call it a whole style on its own.

What Shirou uses is an anti-unit version of the "Shooting Hundred Heads" - a pumelling, high-speed series of 9 strikes. As a side-note, the main version of Hercules is an anti-phantasmal beast, simultaneously discharging 9 dragon-like homing lasers.

Source: Comptiq 2007-03

In Fate/Unlimited Codes, Berserker uses another version of this move as his ultimate move: it takes the form of a series of a hundred consecutive random slashes, with a speed that rapidly increases. This appears to be directly based on the alternate name of the attack, The Shooting Hundred Heads (射殺す百頭).