Top 5 in Top 10 most popular anime of Ufotable.
Fate/Zero
Fate/Zero is adapted from the light novel of the same name written by Gen Urobuchi with the help of Nasu Kinoko (father of Fate/Stay Night). Characters created by Takashi Takeuchi. A four-volume novel series published at the end of 2006 by Nitroplus with copyright permission of Type-Moon.
The content is set 10 years before the 5th Holy Grail War in Fate/Stay Night with the main characters Emiya Kiritsugu (Shirou's adoptive father) and Irisviel von Einzbern (Ilya's mother). The confrontation between 7 Masters and 7 Servants summoned to the real world with the desire to get their hands on the Holy Grail. Love, hatred, and nostalgia for the past bind the souls of legendary warriors in history to be chosen by the Holy Grail to participate in the war.