To summon their "familiars" (sort of like spirit guardians), a bit of blood has to be drawn. Characters are sometimes shown pricking their fingers to summon them.

In the first scene of the anime, there is a ritualistic scene in which Satan gets into the room. He kills all the people in the room, throwing them around, causing them to tear up blood, and eventually bursting into blue fire.

Punching, fist-fighting, and playground brawls, as well as darker imagery like humans being exorcised from demons, characters burning alive, eyes bleeding, and other disturbing images. There are swords and guns are used.

Although most of the violence is supernatural/fantasy action, there is occasional blood. In the last couple of episodes, the violence is more extreme with lots of blood, Satanic sacrifices, and people combusting into blue flames.

Sh*t is used sometimes in the English dub

Frequent swearing

In the subtitles, Satan is usually a potty-mouth, repeating the word /fuck/all the time (depending on the translator). The second opening uses fuck in the subtitles. English dub has shit, bull shit, ass-hole,ass,bastard.

some smoking, a character gets drunk usually and is known to drink a lot.

This show does have some bloody moments and very vicious demons which could be frightening to some.

Character is determined to kill their biological father and become exorcist.