I don't own a darn thing. Inuyasha and everything affiliated with it belongs to Rumiko Takahashi. I am merely letting my imagination run wild.
When she was in the presence of others, Kanna was what they needed her to be.
For Naraku, she was an instrument; his eyes and ears in a world he wished to rule and consume. She was his spy and captured images within her mirror for him to peruse and glut himself on. She was his window, through which he could gaze unto a humanity he had rejected as weak and yet, which defeated him at almost every turn.
When accompanying Kagura, Kanna was a silent wall against which the wind demoness could rave and rant. She would listen to her 'sister's' complaints, her dreams and ambitions and pass no judgment. It was not required of her.
It was only when she was alone, devoid of the company of others, that Kanna was truly herself. With her feet tucked neatly beneath her and gazing into her empty mirror, Kanna was no longer the reflection of other peoples need. She was an empty shell; a blank verse and she preferred it this way. There was peace in this state of being, a state that required nothing, because she required nothing. Alone, she would sit and stare at the reflection in her mirror, watching her own blank gaze look back at her; an endless void reflected into eternity.