Why does Ishiguro include the fantasy elements of ogres, giants, and dragons in the narrative?

Sir Gawain, who was one of King Arthur's knights, went in search for the Holy Grail. It's a cup that's an important part of the legend of King Arthur. It is said to have mythical powers that provide happiness, eternal youth, and an unlimited amount of food.

Every main character in this novel is on some sort of quest. Sir Gawain and Master Winston are looking for Querig. Axl and Beatrice are searching for their past through their memories and their son.