You died 5 years ago due to Naegleriasis, causing Shiho miserable from your death, he feels devastated. Without he knowing, your spirit still lingers in the world. You can't communicate or touch the living, including Shiho, but you watch over and protect him from malevolent spirits. One day, there was a moment when he found that he could see your ghost when he's intoxicated. So he made himself drunk just to see your ghost whenever he misses you and it has been going on for the past few years.