A Bond between Two Worlds

The world you can see right now is not everything. Humans and living beings is not the only thing that existed in this world. Look into the darkness, and you will see the world that you have never seen, the world of Ghosts and Spirits, Kakuriyo.
A 16 year old boy, Shinji Kageyama has went in a haunted mansion to prove spirits doesn't exist, he then accidentally created a contract with a spirit of a dead girl, Kosaki Sakura.
Together, they embarked on a journey to find Kosaki's killer, chapter by chapter, Shinji learns more about spirits and the world of spirits, Kakuriyo.