Riki Hyoudo is your typical highschool slacker and Karate genius who spends his free time conducting martial challenges under a pro wrestling mask. However, unbeknownst to him, he's also the cosmic doppelganger of dimensional devil king lord Byoudo, who learns about a mysterious prophecy related to this oddity and travels to our world to investigate. Byoudo absorbs Riki to get his power, but instead he gets himself absorbed into the boy, and that soon becomes only the first of their problems, as his treacherous lieuetenant Fairy Master Kain initiates a demonic invasion of Earth to kill Byoudo and conquer the planet. Riki and his alter ego will have to team up with aloof demon slayer Toshimitsu Yuuki and Space-Time Continuum inspector Zankan in order to stop the disaster and the rest that will come.
The manga received an OVA adaptation in 1987, Shin Majinden: Battle Royal High School, which enjoyed the curious benefits of having Ichiro Itani in the director chair and Shiro Sagisu in charge of the soundtrack.
This work provides examples of:
- Action Girl: Ryouko is fearless karateka, and although we don't see her fight the bear demon, she is shown completely ready to engage.
- Amazonian Beauty: The final form the Fairy Master takes during the climax is that of a buff nude version of her regular self. That is to say, she becomes bulky, muscular and still pretty hot while also being fairly intimidating.
- Big Bad: Fairy Master Kain is the leader of the demonic invasion of Earth, intending to kill Riki and Byoudo so as to conquer the plane.
- Bittersweet Ending: Riki and his friends are alive and Kain has been defeated, but a lot of people have died in the invasion, including an important demon hunter, and the still evil Byoudo remains within Riki.
- Body Horror: Absolutely rampant, and lavishly animated in the OVA. The only thing gorier than its mutants and demons is the gruesome way they are killed.
- Challenge Seeker: Riki is obssessed with beating other martial artists, the stronger, the better.
- Clothing Damage: Clothes are constantly destroyed in order to show the wearers' nice bodies, both male and female.
- Cute Monster Girl: Kain is quite attractive despite her blue skin, pointed ears and forehead horn.
- Demonic Possession: Several humans become possessed by demons over the course of the OVA, with side effects usually ranging from altered physical structure to significantly increased irritability.
- Fairy Sexy: Downplayed. While it might be a bit of a stretch to call the demon fairies conventionally "cute" they notably have much more attractive designs than the various other monsters that appear. (Granted, that might not be saying much.)
- Hoist by His Own Petard: The Fairy Master stabs Riki with her horn in what she thinks is a mortal blow, but the pain merely knocks Riki unconscious and allows Byoudo to take over his body and use his full power against her. This mistake ultimately costs her both her arms, her head and her life.
- Meaningful Name: Kain, as in the traitorous Cain.
- Naked on Revival: Megumi is naturally naked after Riki uses his powers to completely regenerate her body.
- Off with His Head!: Kain the Fairy Master is killed by having both her arms and head served from her body by the Byoudo possessed Riki.
- Shout-Out:
- The leopard mask used by Riki during his challenges is a clear reference to Tiger Mask. He even wears fingerless gloves and footguards similar to those popularized by Satoru Sayama, the first wrestler that portrayed Tiger Mask in real life, who later became a Mixed Martial Arts pioneer.
- The tall karate club leader named Baba is probably a reference to Japanese wrestling legend Giant Baba.
- The whole plot point of a boy being possessed by a demon yet ultimately being the one in control of its power, who is also forced to face demon hunters and other demons (among them a blue-colored female demon with something personal against him), comes likely from Go Nagai's Devilman.
- One of the most odd and jarring examples of this is a freakin' Felix the Cat poster on the bedroom wall of the girl with the killer teddy bear in the OVA.
- You Are Already Dead: It takes several seconds for Kain to die after being dealt a deathblow by the Byoudo possessed Riki. She even has the chance to curse him one last time before her head finally falls off!Kain: You dirty bastard...! (head slides off)
