The names were so confusing to me. It was in part because of the translation, but still, they're both named Haruka and nicknamed Haru, really?
The ghost girl is Haruka. (Adashino Haruka in full.) Her classmates call her “Ghost Haruka–san” (tho the translation cut this to just “the Ghost” for some reason). And that's regularly cut to Haru as her sister calls her “Haru-nee” and Haru-chan calls her “Haru-san”. And her screenname is “Harusame”.
But what makes it confusing is that Haru-chan's screenname is then “Haruka”! Why‽