Jagaaaaaan

A brief description of the manga Jagaaaaaan:

Shintarou Jagasaki, works as a police officer and lives with his girlfriend. His work slowly and painfully kills him. Everything goes to the point where he ends his days by getting married and living a boring life – a dark future for a dreamer!

But one day, a mysterious monster appears on a train and our hero suddenly discovers that he can shoot from his right hand, that’s where his exciting adventures begin…