The creature standing on top of the evolution system isn't human, but a creature named The Majin. ''Majin Devil'' is a story about a young nerd who fights against monsters of all sorts, and eventually faces Majin, who wants to take his body.

''Majin Devil'' is a 2001 2-book manga series by Creator/OhGreat.

!!This manga provides examples of:

* AFriendInNeed: Haru is Tomoe's old friend from middle school[[spoiler: who got turned into a rokuro-kubi monster by The Professor.]] Guess who comes to Tomoe's aid when she was chased by other rokuro-kubi human-turned-devils?
* AerithAndBob: Kazuya, Tetsu, Satomi, Tomoe, and... ''Harry''?
* AssKickingPose: Dekoppa, a few times. Sometimes with StuffBlowingUp (or otherwise disintegrating) on the background.
* AssShove: Hayashi-sensei did this on Harry... with a lit cigarette.
* BackStory: The first two chapters.
* BadassBookworm: Dekoppa when not possessed. "After all, I am the son of a biologist."
* BadassNormal: Dekoppa, who curbstomps legitimate monsters... ''with science!''
* BattleInTheCenterOfTheMind: in the final chapter. See also [=CMoA=] below.
* {{BFG}}: The Majin had one on his arm as his main mode of asshanding.
%%* BreakingSpeech: The Professor delivers one in chapter 6. Dekoppa's[[spoiler: recitation of the mathematical formula to apoptosis]] in the final chapter has this effect.
* BodyHorror: Too many to list
** chapter 3. The guy also sleeps with women and impregnates them with embryo/spider monsters that either burst out of the woman's womb or emerge from her belly, like the ChestBurster in ''Aliens''.
** The[[spoiler: making of rokuro-kubi type of monsters]], described in loving detail (with live practice!) by the resident MadScientist.
* CurbStompBattle: Well, the titular Majin/Pale Vampire is the embodiment of this. That is, until[[spoiler: he gets his dose of curbstomping from Dekoppa.]]
* EmbarrassingNickname: The protaganist is nicknamed Dekoppa. His real name is Idetora Kazuya.
* TheEndOrIsIt: In the ending,[[spoiler: Dekoppa is shown with a shadow similar in shape to the Majin.]]
* EvenBadMenLoveTheirMamas: The Fuuga Clan chief/sole survivor in Chapter 6.
* EyeScream: The making of rokuro-kubi devils.
* ForScience: The Professor. He likes to study things, and it's no surprise that things get out of hand later on... on the other hand, Hayashi-sensei is this on a much lesser degree. Dekoppa's parents is a questionable case, since they are researchers but it isn't clear whether ForScience is the reason for the ParentalAbandonment.
* GrandTheftMe:[[spoiler: The Professor gets bodyjacked by The Majin in the final chapter, demonstrating his ability to memetically infect people and turn them into an entity under his control.]]
* HitPoints: Dekoppa receives 3652 points of damage!
* HiveMind: The BigBad calls his embryo/spider minions in Chapter 3.
* ImprobableWeaponUser: A Mook uses a giant pair of pliers to kill people. Well, to be fair he uses that plier to throw chunks of rock at bullet-like speeds...
* JourneyToTheCenterOfTheMind: The Professor and Dekoppa embark in one journey into Dekoppa's mind just to see what exactly The Majin is. It doesn't end well, naturally.
* LickingTheBlade: Not a blade, but a window. Like a dog licking a window of a butcher shop. But it's a cute doe-eyed girl who wants a pretty watch in the window. So she licks it...and her saliva melts the glass.
* MadScientist: The Professor, although he is more of a Mad Surgeon playing MixAndMatchCritters with people and demons.
* MateOrDie: "The only reason I wanted your ass was to get at your fallopian tubes." Guh.
* OneWingedAngel: In chapter 4, a guy goes from handsome winged angel to some kind of giant spider monster.
* ParentalAbandonment: Dekoppa's parents, presumably due to their research.
* PettingZooPeople: [[spoiler:Satomi becomes one due to Tetsu attacking and possibly raping her (although in all fairness they apparently weren't blood-siblings) and passing the devil traits to her. The fact that she fed on stray animals instead of people may have had something to do with it]].
* ThePowerOfRock: Satomi's song is powerful enough to deflect a bullet from Majin's BFG. It can heal, and it can send people into their mindscape too. Plus, some of the words are actually pretty poetic. Gigantis' power is similar to this but is mainly for destruction and is not a song.
* RedBaron: Tetsu in his gang days.
* ScrewThisImOuttaHere: The resident MadScientist infecting people with the devil virus tries to flee with two assistants with coolers full of 'precious DNA samples' he used to cook up trouble. He didn't make it...[[spoiler: but it was just a decoy clone]].
* ShadowPin: By demonic babies,no less!
* SpitTake: Dekoppa, when he found out from Hayashi-sensei that Tomoe[[spoiler: is pregnant]].
* UnflinchingWalk: Dekoppa vs Gigantis in the ninth chapter.
* WhatHappenedToTheMouse:[[spoiler: Ashihara's baby/spider nymph. When its 'father' died, did it become dormant or [[NoOntologicalInertia disintegrate in the womb]]? Or did she manage to abort it before any apparent ill effects?]]