This work was originally based on a Japanese manga by Fujihiko Hosono from the late eighties and runs for about an hour total, about the same amount as a short theatrical film. Has no relation to City Hunter.
Bio-Hunter provides examples of:
- Abandoned Warehouse: The main villain is eventually tracked to an abandoned warehouse somewhere in the harbor district of the city and the final confrontation between the heroes and the bad guys takes place there during the last quarter of the OVA.
- Adaptational Attractiveness: Koshigaya in the manga is much shouter and rounder than in the OVA, and looks a bit goofy.
- Adaptational Seriousness: The manga has a good bit more humor than the OVA.
- And the Adventure Continues: After sixty gore-filled minutes of mystery and gruesome violence the good guys finally triumph and walk off into the sunset. Oh, but the virus is still posing a major threat to humanity and Komada has a powerful new demon form to hunt monsters with! Looks like the heroes jobs aren't quite done just yet... thus continues the saga of the Bio-Hunters!
- Badass Bookworm: Both of the main protagonists are highly skilled scientists that just so happen to spend most of their free time hunting down and neutralizing demonic mutants created by a mysterious supernatural virus. Koshigaya is even introduced giving a lecture to a classroom of bored college students.
- Bittersweet Ending: In the OVA. The good guys ultimately win, though Sayaka's grandfather is killed and it's implied that Komada may have permanently lost a part of his humanity to finish off the virus possessing the main villain. Also the disease itself isn't completely eradicated yet, so Komada and Koshigaya still have a lot of hard work ahead of them.
- Body Horror: It's an anime OVA from the middle of the 90s about a demonic disease that turns people into monsters, what on earth else would it have? Special mention goes to the first victim, a woman who grows giant fanged mouths on her tits and gnaws her unlucky guy friend's hand off with them!
- Clone by Conversion: The Demon Virus gradually rewrites the human genome and eventually replaces the cells of the host's brain, erasing their mind.
- Combat Tentacles: Utilized extensively by the Big Bad even after being completely decapitated...!
- Corrupt Politician: Seijuro Tabe. It's even stated by Bokudo that his greed and lust for power is what allowed the demon virus to fully take over and control his actions, leaving him little more than a dead man in a monster's body. Unsurprisingly, he turns out to be the final threat that the heroes have to bring down at the end of the story.
- Demonic Possession: It's heavily implied by Bokudo that the final stage for anyone who contracts the demon virus but is unable to cure or overcome it is this. He calls the state "Devil-Possessed" and claims that it's basically possession by an evil spirit in an undead human host. This is the ultimate fate of the second demon virus monster, the villainous politician Seijuro Tabe.
- Detect Evil: Komada gets involuntarily teary-eyed whenever a carrier of the demon virus is nearby.
- Doing In the Wizard: The Demon Virus essentially does this for a large chunk of folklore and mythology, giving things like vampires and werewolves among others a scientific explanation.
- Fan Disservice: There's a lot of nudity in this one... and pretty much none of it is actually erotic. Boobs growing mouths and eating some guy's hand, tentacles being used to bind the nude female lead, women being stalked, attacked and eaten alive in the middle of the night...
- Healing Factor: Komada has one of these thanks to his condition, recovering from being shot several times with a rifle in a few minutes—apparently it doesn't matter if he's in human form or not.
- Horror Hunger: This is one of the main symptoms of those who have been afflicted by the virus.
- The Immune: Komada contracted the Demon Virus, but turned out to have an incredibly rare immunity that allowed him to tame and control it.
- Meditating Under a Waterfall: Bokudo claims that he does this as a way to "purify and cleanse" his spirit. He's later seen having a discussion with Koshigaya while sitting under a waterfall right before the temple is attacked by a helicopter.
- Monster Misogyny: While the very first onscreen demon virus fatality was a man all of the other victims are shown to be female. This is because the second demon virus monster has already fallen to such a state that the only thing that can keep him together is the live livers of young women.
- One-Winged Angel: Both the hero and the villain go full beast mode for their big final battle at the end.
- Organ Autonomy: One of the weirdest examples ever. Komada's right hand gets blown off in an explosion, flies through the air to grab onto a helicopter's landing gear and is later seen crawling to and "possessing" the female lead so that it can take down the Big Bad at the end of the final showdown... yeah.
- Parking Garage: One of the many demon virus monster victims is a woman who was ambushed inside an empty parking garage and made into a human happy meal. The scene in question cuts to the aftermath of the attack with blood pouring out of her car and the demon virus monster chewing on her liver.
- Product Placement: Done a bit more subtly than most other examples of this trope but still present. A bucket of what is clearly KFC can be seen among the food Komada is chowing down on after being infected with the demon virus and he can later be seen handing Sayaka a can of Coca Cola while the gang is chilling at a rest stop.
- "The Reason You Suck" Speech: Bokudo gives a pretty scathing one to Big Bad Seijuro Tabe right before the climax, telling him exactly how he ended up suffering the fate that he did:Bokudo: The medicine was powerful, it could have dried up the seeds of evil that had found a home in you. But you love power! You love authority! You never gave the medicine a chance! Yes, the truth hurts, doesn't it?Tabe: Shut up! This is nonsense, I won't listen!Bokudo: If you had let it work you could've become human... but now it's too late, you're just another victim!Tabe: You stupid old man!Bokudo: You are no longer Seijuro Tabe, no longer a human being... but a grotesque monster feeding on the innocent!
- Red Eyes, Take Warning: Komada's deadly monster form has very menacing red eyes.
- R-Rated Opening: The OVA opens up with a nude couple having sex which quickly takes a turn for the nasty when the woman morphs into a horrible monster and tears the guys arm clean off.
- Spider-Sense: Komada's eyes start tearing up when he's in the presence of the Demon Virus.
- Superpowered Evil Side: After being infected by the demon virus during the first ten minutes of the OVA Komada gains the ability to temporarily transform into a giant beastial state that gives him extreme power and agility but is also threatening to slowly take over his mind and body. By the end it's implied that he and the demon virus have undergone some sort of fusion or synchronization, making him no longer fully human but allowing him to retain his personality and humanity.
- Super-Strength: Komada in the manga has a degree of this even in human form.
- Teacher/Student Romance: Koshigaya has no problem getting intimately involved with his students, though it's implied that Komada is much more reserved in this regard and looks down on him for it.