Responses
for the mushroom thing, i think they were poisonous mushrooms [like, he did find them randomly in a forest] and it was added for humor points [this manga does that a lot, adding bits at the end to lighen things up]
I remember that particular priest scene. It was from a movie called “The Exorcism of Emily Rose” so I don’t think it is as significant as you may think.
Honestly, there must be more to him being a homicide investigator and a murderer, the way his eyes twitch whenever he encounters a bad guy, the way he quite literally did gymnastics over a mushroom, the way his eyes rolled way back, i've read the older chapters a long time ago so i don't remember any other behaviours but i believe that priest movie has something to do with it.