Sankaku Mado no Sotogawa wa Yoru

Kousuke Mikado has been able to see spirits since he was a child. Frightened by them, he wears glasses to try and hide his ability. One day, while working at a bookstore, he attracts the attention of Rihito Hiyakawa, an eccentric medium who believes they are meant to be together.

Hiyakawa throws Mikado into the world of the paranormal and promises to help him overcome his fears if he sticks with him. As they explore, they find a mysterious curse that leads to the same person - "Erika Hiura". What is this person's goal and how do they connect to Mikado and Hiyakawa?