Tatsumi is a delinquent with a good heart, but he sure loves to fight and kick the crap out of everyone.
Guts doesn't let anyone stop him on his path to revenge. With his 2 meters long sword he will cut his oponents in half.
Lucy has a split personality and doesnt come out much to the surface. But when she does she is a unstoppable killing machine killing everyone in her sights if she feels like it.
Yuno may seem like a nice and cute girl, but be aware of her yandere killing side. Nobody is allowed to come between her and her love Yuuki.
Alucard aka Dracula himself has no problems eliminating anyone who stand in his ways. Even if it are policemen doing their job, Alucard will kill them in gruesome ways.
Momonga aka Ains is a virtual reality video gamer stuck inside his undead game character. Alongside of being stuck in that undead body his human emotions seem to have almost completely disappeared. So altough he has saved a town and several people he also has no issues disregarding human lives for his own gain. Even to the point of murdering adventurers and tens of thousands of soldiers..
Fujiki is the "good guy" ...sort of. Because samurai in the past weren't good guys. Fujiki is a cold killing machine blindly obeying orders. Anybody disrespectfull against his boss will get beat to death while he has a cold and lazy look in his eyes.