"The Human Eater Laboratory Murder Case" is the first case arc in the 20th Anniversary Series of The Kindaichi Case Files.
After Kindaichi and Miyuki are invited by Mayu Midorikawa, a former classmate of theirs, for a visit, they make their way to a bio-research lab, where Mayu works, which is located in Hitokui, a remote village with low population count. Just as they ready themselves to settle down inside the lab, a serial murder case is underway.
Tropes include:
- Alliterative Name: Mayu Midorikawa.
- Bath Suicide: The second murder victim is found dead in a bathtub with a slit wrist. This is subverted, however, as Kindaichi reveals during Summation Gathering: The target had consumed beverages laced with sleeping medication without realizing until it was too late, allowing the culprit to manipulate the setting and kill the target while making it appear as though the target had offed himself.
- Catapult Nightmare: Early in the case arc, a chapter begins with Kindaichi's mother who's about to kill him after telling him the family financial circumstances have gotten worse right as he's Held Back in School, with Kindaichi screaming before waking up on the bed of the bio-research lab he's staying within and realizing the whole scenario was All Just a Dream.
- Conveniently an Orphan: The culprit was abandoned by their own parents soon after birth before being placed in an orphanage and raised there.
- Deceptive Disciple: Mayu's father turns out to have been a victim of murder that was done by two of his bio-research assistants, both of whom end up as murder victims in this present-day serial murder case.
- Delayed Reaction: One officer in the local police force talks to Kindaichi about inspector Tawarada vouching for his deductive prowess before they arrived at Hitokui Village, which explains their ready willingness to let Kindaichi poke around in every crime scene. It takes some conversations before Kindaichi realizes that the local police officers managed to communicate with inspector Tawarada in the first place despite all conventional communication devices within the area being unavailable, which prompts the cop Kindaichi talks to to inform him about the devices they use for communication.
- Disappeared Dad: Mayu's father died two years ago.
- Disney Villain Death: When the first victim is found dead on the ground, the survivors surveying the area find a door on the third floor being propped open, which quickly clues the survivors in that the victim in question fell from the third floor and ended up with a snapped neck, dying upon impact instantly.
- Don't Call Me "Sir": Mayu tells one of the lab researchers not to call her "Chief" in front of her friends like Kindaichi and Miyuki at least once.
- Dying Clue: Mayu's father left a clue resembling an algebraic formula (3a+3i+3e=M) before his death. Said formula turns out to be a cryptic list of the names of the people who were involved in his murder, as the names of the targets are "*a*i*e" (with * being a consonant) and "M" is for "Murderer".
- Dying Town: Much of the economy in Hitokui Village has been dependent on a bio-chemical research lab, so there was more population within the village when there was more funding for lab research(es) during WWII and the population decreased after much of the funding for lab researching got pulled out or dried up after WWII. Nowadays, about half of the buildings in the village are boarded up and/or showing some other signs of vacancy.
- Foil: Despite being intelligent just like Kindaichi, Mayu is diligent and studious, whereas Kindaichi is a Brilliant, but Lazy Apathetic Student, as the flashback scenarios of their days as junior high school classmates quickly illustrate at the start of the case arc.
- Friend on the Force: Inspector Tawarada serves this role in his brief appearance in this case arc by vouching for Kindaichi through his phone conversation to the local police in order to allow him to help with the police investigation in this murder case.
- He Knows Too Much:
- The third murder victim was initially not the intended target, but he discovers a device the culprit happens to carry at the time after ambushing the culprit with the original intent of stealing a lab key before contacting the culprit privately sometime afterwards, with the intention of getting money out of the culprit via Blackmail. All that he manages to accomplish is only in getting the person targeted later on when the culprit is the one doing the ambushing, reversing their roles, and the culprit proceeds to have the target murdered soon afterwards while trying to make it look like the victim died by self-inflicted hanging.
- Downplayed with the last one of the intended target, who confesses to only have witnessed the other two intended targets murdering Mayu's father and making it appear as though he had offed himself before joining the other two in keeping silent about the murder both due to their personal financial hardship and to avoid being a murder victim as well.It was two murderous men against me, you know! One wrong step and I'd have been killed as well!
- I Don't Like the Sound of That Place: The bio-research lab that is the center of this murder case arc has been given the nickname "the man-eating research lab" due to the sheer amount of researchers who were Driven to Suicide within the lab in question, especially during WWII, when the lab was at the apex of its funding and, therefore, operational capacity — and the amount of researchers who had offed themselves as well when the war became too drawn-out for the researchers suffering mental breakdown to continue any longer.
- The Killer Becomes the Killed: Each Deceptive Disciple who was directly responsible for having murdered Mayu's father ends up as murder victim in this serial murder case.
- Man on Fire: This was how Mayu's father was murdered two years ago, as his Deceptive Disciple (two, in fact) immolated him to death.
- Never Suicide:
- None of the victims in this murder case died of suicide. Even the closest example to this is the result of the culprit's deliberate planning to nudge the intended target into panicking and running out the door of the third floor into the now-nonexistent corridor, falling to their doom.
- In addition, Mayu's father turns out to have been a murder victim himself, something Mayu herself has correctly suspected: His killers had arranged to Make It Look Like an Accident, as Kindaichi reveals during Summation Gathering.
- No Honor Among Thieves: The last intended victim arrives at Hitokui Village with one other guy with the intention of speeding up the search for Mayu's father's research findings. After ambushing the culprit like the last intended target instructs, the accomplice suddenly wants out of the deal, and Kindaichi surmises during The Summation that said accomplice finds a device from the culprit and intends to Blackmail the culprit for money — not that it does the guy any good in the end, because the culprit ends up agreeing to the condition only to get the accomplice killed for discovering something incriminating instead.
- Orphan's Ordeal: Mayu is rendered an orphan after her father died (her mother was deceased some time ago earlier), and the culprit, after being abandoned by one's own parents right after birth and raised in an orphanage, always considers Mayu's father their surrogate father figure after being acquainted with him. Some time after the passing of Mayu's father, Mayu hacked into the email archive of the intended targets — she knew who they were after quickly solving the Dying Clue, being a Teen Genius herself and all — and discovered the Awful Truth behind her father's demise and spent the following two years coming up with a plan to have all of the intended targets Lured into a Trap. However, Mayu only manages to succeed up to inviting them to Hitokui, only to lose her nerve at carrying out her revenge plot; the culprit does the rest without Mayu's knowledge right up until the time of the Summation Gathering.
- Parental Abandonment: The culprit was abandoned by their own parents soon after birth and became Conveniently an Orphan as the result.
- Plot-Triggering Death: The death of Mayu's father kick-started the murder case arc. As he died two years prior to the present-day case arc scenario, he also counts as a Posthumous Character.
- Poisoned Chalice Switcheroo: Happens once Kindaichi reveals connections made by victims on the murder case and points out that there is still one the killer hasn't killed. The killer initially plans on making the last victim's death through poisoning the target's drink, but Kindaichi right away blurts out that he had already switched the victim's drink with the killer's and asked for all remaining suspects to drink all at once to reveal who the killer is.
- "Shaggy Dog" Story:
- Two of Mayu's father's bio-research assistants became Deceptive Disciple and committed the murder after he stated his intention of donating the bio-research finding on the internet due to their Greed, as they wanted to make money off said finding instead. The two assistants' "recruitment process" in getting the other, who had witnessed the murder at an inopportune moment, to cooperate with them was by reminding the latter of the potential payout via patenting and selling said bio-research finding, after they had already filched a memory card containing information regarding said finding. The three proceeded to open the chip the next day, hoping to find more detailed information... only to be greeted with security measures they couldn't unlock or bypass, so the whole murder plot ended up All for Nothing after all — except to get themselves targeted two years later.
- In the present day, the "recruited" person burns the suspension bridge and causes the village to become a Closed Circle, in the hope of buying enough time to find the bio-research data. Not only does the person end up unable to find the desired item, the bridge-burning also serves as an Unwitting Instigator of Doom as well due to the culprit, upon witnessing the burned bridge alongside everyone else, becoming incentivized to carry out the murder plot, with the bridge-burner nearly falling victim to murder, too — the only reason the intended target survives is due to Kindaichi, having realized what the killer's murder tactic is and who's being targeted, pulling a Poisoned Chalice Switcheroo on the culprit right before Summation Gathering is to take place.
- Slipping a Mickey: During the Summation Gathering session, Kindaichi surmises that the beverage being consumed by the second victim had been laced with some sleeping drug in advance, so that the culprit could exact murder on said victim when the timing was right.
- Smart People Wear Glasses: Mayu is an eyeglasses-wearing Teen Genius who works as the chief of the bio-research lab in the present day.
- Teen Genius: As Kindaichi and Miyuki's memory shows, Mayu was noted as an intelligent and diligent teenager back when they were classmates in the same middle school they were attending two years ago. In the present day, Mayu works as the chief of the bio-research lab.
- "Too Young to Die" Lamentation: Early in the case arc, Kindaichi's mother is about to kill her son with a sharp cutting knife after telling him the family financial circumstances have gotten worse right as he's Held Back in School. Kindaichi screams "I'm too young to die!"... before waking up with Overly-Nervous Flop Sweat, shaking all over in his body, and realizing that his dying moment was All Just a Dream.Kindaichi: What a heart-stopping nightmare! I thought I actually died!
- Unwitting Instigator of Doom: Kindaichi reveals during Summation Gathering that the last intended murder victim, by burning the suspension bridge with the intention of seeking out the bio-research data, makes the village where they stay a Closed Circle, which, in turn, prompts the culprit to put the murder plot into motion.Kindaichi: [to the last intended murder target] What you did... ended up encouraging the culprit!
- Wanting Is Better Than Having: Played for Laughs. As Kindaichi and Miyuki set out to return home at the end of the case arc, Kindaichi suddenly remembers that he has yet to ask Mayu for the answer of a puzzle Mayu had given him before she dropped out of school to work at the bio-research lab, but, luckily, Miyuki had received from Mayu a sheet of paper containing hints regarding the puzzle during the case arc and hands it to him. Kindaichi solves it at once... and finds himself flabbergasted by the answernote .Kindaichi: Seriously?
Miyuki: Eh? What? What does it say?
Kindaichi: Nah, it's nothing!
Miyuki: Eh? What is it? Tell me, Hajime-chan!
Kindaichi: Forget it. It really is nothing!
