Fate/Zero (2011) is a prequel to
Fate/Stay Night (2006).
Fate/Zero (2011-2012) will be separated into 2 seasons, taking a break between episode 13 and 14, for animation enhancements. the story took place 10 years before
Fate/Stay Night (2006). it focused on the events of the 4th Holy Grail War, from summoning the 7 heroic spirits to battling for their lives and victory. the war was a contest among the 7 spirits to obtain the power of the Holy Grail, which will grant miracles. the Einzbern family was determined to achieve success after the previous 3 failures.
the first few episodes slowly refreshed our memories of who everyone was, though i long forgotten its details. the spirits may seemed vividly familiar, but as for their masters of this generation, was far from being familiar. the biggest difference between the 2 anime, was how the master view their servants. in this anime, the heroic spirits were merely magical tools for its master to achieve victory; where else in
Fate/Stay Night (2006), the spirits were considered friends, where master struggled to keep their spirits safe from harm. for having as much as 7 pairs of characters, it was expected to be slightly confusing for some, but still interesting enough to watch despite starting out being slightly slow-paced.