Sahyeong Jiphaenggwan

A hero should never kill anyone, not even the worst of villains. Gangyu could never understand why his team of heroes lived by those words, but he tried his best to do the same… until the villain who wiped out his squad killed his brother in prison. Gangyu breaks his vow and enters Ruculus with permission to kill as the prison’s executioner. Now, he must fight his way through the villains to kill the worst of them all.
(Source: WEBTOONS)