It is clear from the way that Mangan's sister is presented that the narrator is interested not so much in Mangan's sister herself, but in what his fevered, romantic imaginings make her. The very fact that Mangan's sister is never given a name, and that he is able to develop such an attraction towards her without ever exchanging a word with her strongly supports this view. However, the behaviour of the boy towards Mangan's sister borders on the obsessive, as he appears to be always watching out for her. Note how she is presented as he peers through his window at her when she calls her brother in for tea:
She was waiting for us, her figure defined by the light from the half-opened door. Her brother always teased her before he obeyed and I stood by the railings looking at her. Her dress swung as she moved her body and the soft rope of her hair tossed from side to side.
The way in which Mangan's sister is often presented with light behind her suggests that there is something angelic about her in the narrator's mind, which adds to the sense that Mangan's sister exists less as a real person in her own right but more as a receptacle of the narrator's dreams and romantic imagination. The stage is therefore set for when she does actually speak to him for the narrator to view himself as a knight charged with an important quest in order to gain a token for his lady love. However, as the narrator realises at the end of the story, his "relationship" with Mangan's sister is built on nothing substantial except his own dreams and imagination, and this is supported through the vague and indistinct way in which her character is presented in this short story.