What is this manga about a boy with special eyes recruited by 3 girls to hunt murderers?
It's definitely Deathtopia.

Here is the picture of the main character on the color page of chapter 1.



This is a scene near the end of chapter 1 of the guy who eventually murder everyone in his family and eats ramen while sitting on the couch, as revealed in chapter 2 and 3. At this point in time, the main character had yet to see the true shape of the shadow, and he only managed to made out the scythe-shaped shadow in chapter 2.



The three girls who scouted him at the end of chapter 1: