This is the 5116th most frequent Turkish word.
hikayesi
"Story" or "narrative."
Here, 'hikayesi' (his/her/its story) is used to denote the narrative of the novel ('roman').
Bu romanın hikayesi çok etkileyici.
The story of this novel is very impressive.
In this context, 'hikayesi' refers to the story or life journey of 'onun' (him/her/the subject).
Onun hikayesi beni derinden etkiledi.
His/her story deeply moved me.
'Hikayesi' describes the individual stories ('hikaye') contained within the books ('kitaplar').