Two-Way One-Sided Attraction: Tsukasa x OC x Kou

Yashiro Ruri is the younger twin sister of Yashiro Nene who wishes for one thing, to have a friend like her sister does. Someone who understands her, can relate to her life experiences, be there to cheer her up when she's feeling down, and most importantly, to share a special bond with.

What would happen if her wish was granted but instead of friends, she now has two lovers instead?

Or

In which Yashiro Nene's little sister has a crush on both an inexperienced exorcist and a psychopathic little ghost and doesn't know who to choose.