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Nightmare Fuel: Fist of the North Star
This classic has its share of Nightmare Fuel. Interestingly enough, at the time it was first released, it was aimed at kids. Nowadays, people would say that this work is meant for an older audience.
The nuclear war, as shown in the original movie. It's on par with Barefoot Gen, with showing people being graphically vaporized by the nuclear bombs, loads of Eye Scream, and people so burned that they resemble shambling zombies before they finally fall over and die.
The fighting style of Hokuto Shinken (can be translated as "North Star God Fist" or "Big Dipper Divine Fist") is this. It consists of the practitioner hitting the pressure points of a person. It can be used for healing, which both Kenshiro and Toki demonstrate during the series, but when it is used to kill, it often results in various horrifying effects such as hands blowing up, heads exploding, the whole body exploding, causing someone to uncontrollably walk backwards off a skyscraper, separating a person's skeleton from his skin, causing a person's body to feel like it's covered with bare nerves, and the list goes on. Oh, and the person on the receiving end will often be in agonizing pain as he dies from one of these effects. The story itself acknowledges that this is a terrible fighting style that must never be misused on people, or else it would destroy the world. As events in the story show, it wasn't kidding.
The fighting style of Nanto Seiken (can be translated as "South Star Holy Fist" or "South Dipper Holy Fist") is this for a different reason. Hokuto Shinken destroys enemies by hitting pressure (in other words, from the inside out), while Nanto Seiken simply destroys enemies from the outside in. A practitioner of this style will have fingers as sharp as swords, and can either stab you, as Shin graphically demonstrated on Kenshiro, or slash you to ribbons with air pressure, as Rei does to his enemies.
The fighting style of Taizan Tenrouken (can be translated as "Mount Tai Sirius Fist") is a terrible fighting style. Ryuga is the only practitioner of this style, and that's a good thing. With this style, he scoops the chunks of his victims' flesh while leaving them with a feeling of bitter coldness. They feel cold, not necessarily because he's freezing them, but because he scooped out their nerve endings. Kenshiro himself said that this is a terrible style. When the guy who can make your head explode just by touching a pressure point actually says this, that really tells you something.
The fighting style Hokuto Ryuuken (can be translated as "Big Dipper Shining Stone Fist") may sound like a cool style...until you see it in action. One teacher of the style, Jukei, used it...and paid a terrible price. Apparently, it put him in a state similar to being on drugs. While under the influence, he became demonic-looking, with bulging veins all over his body, his eyes being covered with veins, and emitting purple smoke breath. He also killed a lot of people and caused a lot of destruction while under the influence, and Ryuken had to hit him with pressure points on the neck to snap him out of it. Oh, and Jukei hadn't even surrendered himself completely to it by that point! Oh, and here's the kicker...Jukei didn't even remember what he did while he was on a rampage, and Ryuken had to tell him that during his rampage, he killed his own wife and child. This is the reason the plotline focused on killing off everyone who learned that style.
Jagi, the first major villain in the series to use Hokuto Shinken, who showcases just how horrible the style can be when used for evil, even though he is not a true master of the style like Kenshiro and is the biggest coward of the series. Then he takes off his mask and... SWEET MERCY◊!
A large majority of the villains embody this trope. They look as ugly as sin, and have the personality to match. Some of them seem to be as large as a house or 10-storey-building, and that's bigger than Kenshiro, who is six feet tall. They go around robbing, raping and murdering people. They don't care if women and children are among the men they target. They will also not listen to reason at all. Indeed, one must wonder if they were good people before the nuclear war, or if they were always like this. In fact, with a lot of them being so big and ugly, one must wonder how they got into bomb shelters to survive...and if anyone else in the bomb shelters survived with them. On the other hand, since they're so evil, heartless, and monstrous, you will be fine with Kenshiro using his scary Hokuto Shinken on them.
Viceroy Jakou. He doesn't actually do that much in terms of fighting, but it doesn't make him less scary. First, he sports this big mad slasher grin almost all the time. The fact that it's based off of The Joker's grin from Batman really doesn't help. Second, he shamelessly uses his adoptive brother Falco to do all his dirty work. In fact, he had tried to have one of the twins Lin and Lui killed off when they were only helpless infants. He claimed that a prophecy stated that twins would cause chaos, but it seems that he didn't really care about this prophecy so much as he just wanted to have an infant murdered for kicks. Finally, he tries to have his own adoptive brother murdered without a qualm. Even a Non-Action Big Bad in this story can be scary.
Kaiou. He happens to be very good at Hokuto Ryuuken, and has become so demonic that he has to wear armor not for protection, but to keep his evil Battle Aura contained. It goes without saying that if the armor ever comes off, horrible things will happen. At one point, he murders his own little sister Sayaka, just to manipulate her fiance Hyou. It makes you wonder what it must have been like for her to live with this guy. He also captures Rin and states straight out that she will bear him his son. He's at least seven feet tall and pretty wide, so how Rin would be able to bear him a child, willing or otherwise, is a nightmarish question to think about. The fact that she was on a bed and he was slowly and menacingly approaching her at one point certainly did not help matters.
Alf of the Hourglass. You might think he's just an imitator of a bull-fighting matador...until you punch his poisoned cape. The good news is that the poison itself will not kill you and will wear off in a short time. The bad news is that the poison will cause you to experience at least double vision and disorient you, in which time, Alf will charge to stab you with his weapon. Here's a little tidbit: in Real Life, there are poisons out there that can go through your skin and into your bloodstream; the official name for them is contact poisons. So the idea of getting poisoned just because it ended up on your hands is not as far-fetched as you might think.