Fate/stay night (2006)

S1E3 Opening Act

Shirou finds himself utterly bewildered after encountering the graceful warrior known as Saber, who has chosen him as her Master. Just as he begins to process the surreal turn of events, Saber jumps back into battle against Lancer. However, Lancer decides to exit the conflict before it escalates. Soon after, Saber confronts Rin and her servant, but ultimately agrees to Shirou's command to hold back. It’s at this moment that Shirou discovers the reality of the Holy Grail War and the unexpected role he has taken on in it.