Jii-san to Boku no Jiken Jou

I, Itsumi Nakadera, have been living in an institution since my parents' death. Two years ago, when I was about to be adopted by a wealthy family, my grandfather Itsuki came looking for me, but frankly, I had no intention of going with some random old man I didn't know. The reason I changed my mind was because I was annoyed by the way my grandfather looked at me, as if I was some sort unusual creature. Since then, I've started living alone with my grandfather. He is a super-humanly quiet and unsociable man, but he always gives me advice on the various incidents that I come across... A grandfather and his grandson team to up solve many mysteries together in this slice-of-life detective story! (Source: Group Zero, translated)