Murahagane

Murahagane (叢鋼 -ムラハガネ) is a one-shot manga series by Manabu Yashiro. It was serialized in Weekly Shonen Jump.

Plot
Crimes committed by "Kaijin," superhumans produced by technology, are on the rise in Tokyo. Shibasaki Ken and Momoyama Reiji are assigned to work together to solve a recent serial killer case. In some ways they complement each other nicely: Shibasaki is an expert tracker, and Reiji is an expert at combat. Their personalities, however, do not mesh at all. Shibasaki would rather skip work to flirt with girls, while Reiji is violently overzealous about his job. Will they be able to work together to solve the crime before more lives are claimed?