Ninja to Gokudou

Ninja to Gokudou (忍者と極道, Ninja to Gokudō) or Ninja vs Yakuza is a Japanese manga series written and illustrated by KONDOU Shinsuke.

Plot
Shinoha is a boy (ninja) who can't laugh from a trauma, and Kiwami is an elite company employee from the outside, but in reality controls a yakuza group. The flames of war between ninja and yakuza runs for over 300 years. Who will survive, the ninja or the yakuza.