Vinland Saga

It starts as a Viking revenge epic. A boy named Thorfinn watches his father die at the hands of a mercenary and spends years trying to kill the man responsible. Then Yukimura does something most action manga never attempt: he lets the revenge collapse, strips Thorfinn of his purpose, and sends him to work as a slave on a farm. The back half is about a man who built his identity on killing trying to figure out what a life without it looks like. It draws on real history, Knut's rise to the English throne, the dream of a land without war, and treats violence as a problem to solve rather than a thrill to deliver.