I recommend to read this. Is fun!!! But it's going to be a long story. Is has like 100+ ep (you can read in webtoon Thailand too) but it's not in English the MC main weapon is a gun too (つ≧▽≦)つ it will be about immortal//hell// and they will be a lot of blood scene too(☆▽☆)
Hell Warden Roruv