Flowers for Chronous(2013)

Kimi no Chronous

Soju Sagara is a lonely, shy high school student employed by a secret organization to investigate violent incidents involving a weapon known only as "SOWN." Teaming up Leon, who has the appearance of a young boy (though in reality is far more) and the Void Association, the pair investigates numerous cases of chaos, each time learning more about the private traumas that fuel our demons.

(Source: One Peace Books)