Shock! The Academy Murder Case?

I overheard Zeke Giratina and Orochi, who suddenly started liking Yamucha Aranemu, declaring they'd team up to solve this terrifying murder case.
"The culprit's committing murders right out in the open at the academy... I'll smash 'em!"
"One shot from my Requiem here can even kill a witch."
Their level of determination was so intense, I thought we'd all be dead if we got caught.
Come to think of it, Orochi calls Ephemera Flash "miss," so maybe they're from her household? I figured they were just some airheaded kid (ranked 228th) who wore cute snake puppet gloves and walked around with their cleavage wide open for "ventilation."
Is their public image different from their true nature? I thought we were close, but this unexpected side surprised me a bit.
Well, you can't know someone's deepest thoughts... Even close friends have secrets.
Does that mean I just gained a secret from my friends today too?
"Who would've thought I had a talent for killing people..."
<Let's phrase that nicely. Say you have a talent for perfect crimes.>
"Blood doesn't lie, huh?"
<Don't let your hair grow out, please—don't awaken the witch inside!>
Grand Duke (Change) was making a huge fuss, but thinking back, if he hadn't smashed that guy's head in a fit of rage, things wouldn't have escalated this far! One impulsive act snowballed way out of control, and with no brakes, I couldn't stop.
...Even if I tell myself repeat students aren't human—just artificial lifeforms without souls or spirits, disguised as first-years and infiltrating like monsters—what's my gut gonna say...?
"Once I get used to it, there might be no turning back... Normal people feel guilty after killing, right...?"
<It's some race thing, so don't overthink it? Okay?>
The thought that I could do it more cleanly next time lingered in my head, refusing to fade, so I let out a sigh.
Do I really need this kind of talent as an academy student?
"Our first-year academy is now under threat from an unidentified black mage..."
An unknown mastermind hiding in the academy since before I enrolled! Looking back, there haven't been any real threats yet! I knew they planned bad stuff, but since they haven't done it, it feels kinda iffy!
"During midterms... I was a nuisance to everyone!! To protect my friends' finals!! For justice, I'll even kill if I have to!"
<Aah... Kiryu... Is that you...? The fool who chased justice...>
Grand Duke had given up and was just letting me do whatever.
First, I used witch powers to slip through a dimensional rift—then tracked the aura of [Black Magic] to find another repeat student.
The first one was brewing illegal drugs. Selling aphrodisiacs and laxatives... so insidious.
The second was illegal smuggling. Not even hiding treasures—just leaking exam papers and fudging grades. And they even had the spices the first one was after.
So the third must be connected somehow?
"Kihihihi... It's done!! This red color!!"
They were in the dorms, so I dimensional-hopped over. The room was drenched in blood-red.
I hesitated at the sight of them blissfully dipping their hands in some unidentified red liquid.
"Drag 'em into the mirror world and it's over!!"
<Even Merhen doesn't have a mirror world, Kakyoin.>
I reached through the mirror, grabbed their nape, and kidnapped them.
They were wearing some rubber gloves... My face burned. Gunpowder chemicals maybe? But... no choice!
"They're not human, right?!"
<No, they're not.>
When disposing, I make sure to confirm properly!

"Huff... huff... Weird... Stabbing with a knife when excited didn't tire me out..."
I dragged them to an empty lot behind and buried them with a shovel—that part was fine, but they were on the brink of death.
My heart felt like it would burst; breathing was hard.
Collapsed and exhausted, I thought I'd die if I closed my eyes right then.
"What would Mom do in a situation like this...!"
<I dunno, she hates leaving bodies behind.>
Your mom always aims for total victory. She usually cleans up without leaving corpses.
That sounded tempting, but burying the dead feels right, doesn't it? I still think I haven't lost my kindness and humanity!
<So one left—whaddya wanna do?>
"....."
Staring between the dirt and shovel, I suddenly remembered I hadn't eaten.
"Sniff."
I blew my nose and opened my fat wallet, pulling out cash.
★★★
"Now for the final victim."

"These wounds are razor-sharp, aren't they? As a predator race, my instincts tell me."
"How?"
"This is either the work of a monstrously strong crow from hell... or someone skilled in anatomy. Death by blood loss, but they used drugs to evaporate the blood internally."
Orochi was impressed by Zeke's deduction.
"Then! The culprit's trying to frame Wiyu Witchcraft!"
"Ah, yeah...!"
One repeat student in the dorms was found buried in the lot behind. Hard to pinpoint when, but timing-wise, Wiyu was being accused as the perp right then.
"This clears Wiyu's alibi perfectly."
One of the few precious friends helping connect me with Yamucha. Sure, that pointless giant chocolate milk generator subconsciously seduces Yamucha, but still a good friend.
—Help Wiyu and score points with Yamucha... What a perfect two birds with one stone!
"All the dead repeats were first-years for 4+ years. The first two caused so much trouble they got demoted?"
"Promoted then demoted?? How? Demotions exist?"
"They sold drugs—demoted for drugging people and causing nuisances, probably."
I told Orochi they deserved any grudge killings.
No need to look far—some rich pig offered crazy deals to drug Wiyu with aphrodisiacs since she was his type. Total money fiends.
"Planning to destroy the academy...? Never happened before—why target Witchcraft?"
Investigation confirmed it was someone with a grudge against Witchcraft. Artificially inflating first-year repeats to hide, amassing cash.
Then Wiyu enrolls and acts all "emotional."
"Homunculi made with [Black Magic]. Creator's subconscious imprints on 'em. Ultimately, revenge for someone Wiyu got to."
"Suspects?"
"All four dead repeats took [Herbology]—weird if you don't suspect."
Zeke contacted the [Divination] professor to avoid issues with the deaths. A prof with unchecked power beyond even the principal in academy history.
The murdered first-year repeats were instantly [data-erased] from records. Fake commoner IDs anyway... So even if people died, no "deaths" occurred—a miracle!
"Wiyu's innocent!"
"Even if she killed the first, she's innocent—don't forget."
"?"

Zeke called me out, so I braced for the worst—innocent? She prepared a perfect alibi? Erased their fake student IDs? I glimpsed the academy's dark side and felt down.
Killed four repeats—really okay to forgive?
"And the mystery's solved!! The culprit's the [Herbology] professor!! You!!"
"Kuh...! If the homunculi hadn't reacted to Witchcraft and gone rogue...!"
"No laundering or embezzling—explain what smuggling as a first-year was for!"
"....Can't say."
"I see."

Bang bang bang bang—!! Merciless six-shot barrage...!! Tossed the spent revolver, drew new ones in both hands for confirmation kills...!! Already overkill, but Orochi pulled the trigger without mercy, leaving no room.
"You actually shot!!"
"Gaaahhh!!"

Detective and true culprit both shocked...!! Wiyu broke into cold sweats thinking she could've been the target.
Even as a prof, tanking a full revolver plus six more? Normal people can't.
"Dwarven custom .50 cal revolver and still alive?"
"No, that's excessive killing intent."
"For Ephemera miss's honor, I'd shoot the crotch too, Chocolate."
"Lemme kill you instead..."
Just let 'em finish as the culprit... Too gruesome to watch.
The [Divination] prof muttered about removing one grad student hopeful amid it all.
"Heh... So this day came..."
"Why're you fine?"
"Because!! I'm a hero summoned to this world!!"
"Herbology prof's a hero?!"
The prof, sprawled and sobbing, muttered that without Wiyu's enrollment, it'd just be more first-year repeats.
"Sorry... I suffer every day... But I needed money."
No wonder the generous grading—guilt over it?
<Hero from another world... How'd that happen?>
"Living fine, some god drags me here to beat Demon King Aris Witchcraft."
Everyone nodded, understanding the resignation to prof life.
"Hmm... From four years ago? Why suddenly this?"
Next, the [Divination] prof interrogated. Normal before—how'd they turn dark?
Head bowed, trembling, the prof yelled.
"I wanted kimchi!! This world has none!! Sob sob."
<Ah...>
Grand Duke, hell's duke who contracts other dimensions, sighed knowingly. I don't know the dish, but otherworlder—homesick food drove this? Good no nuisance to first-years!
"Glad you feel guilt."
<Does he?>
"Otherworlders can't return home?"
Grand Duke explained a limbo dimension for dimension-bounced folk like the prof: [Nexusium]. Even Aris can't cross unknown dimensions—only linked ones. Even he couldn't—
"Opened it though?"
<Yeah, do whatever.>
Just wished for the prof's dimension door, and it opened easy. Everyone stared dumbfounded, but hey, good result.
"Prof! Go home!"
"Uh... that...!"

"Better stay as prof? No mana there—can't use magic, just jobless old guy..!"
"Sorry, gotta vanish for perfect crime."
<Hide him.>
Tearing up, I chucked the Herbology prof back to his dimension. Colorful folks helped him up beyond the portal—heartwarming.
Happy ending—great...!
"How many profs you sending away..."
[Divination] prof shuddered behind, but minor issue.
Thus, the [First-Year Repeat Student Serial Murders] at the academy ended.
Grudge deep enough to drag an innocent civilian hero here as revenge pawn. Son ended mom's inherited feud—fine conclusion.
Hope he eats tons of kimchi there happily... Minor detail: came at 17, leaving at 32. Mana-less but prof skills—he'll manage!
Thanks to true culprit Wiyu Witchcraft and ace detective Zeke Giratina, peace returned.
Training camp scores went negative, but we'd overcome. For finals, everyone studied normally together.
Shared summary notes, organized stuff. Tips from third-years and profs, solved predicted exams.
"All together" teaching Wiyu boosted everyone's grades big time.
Again: everyone studied hard together.
Excluding 4 dead repeats: 200 left. Plus current 750 first-years = 950 total...!!
Wiyu Witchcraft's rank competing with them:

Everyone's hard study miracle... Wiyu prayed "good luck on exams" for all—no harm unlike midterms. Wide-area wish excluding self: granted.
Plus, Wiyu's top subject: Herbology. Prof gone, so...
"Screwed."
200 extra repeats drop rank miracle descent..!
"Getting... farther... and... away... ♬ 200 repeat adds land Wiyu Witchcra... 950th!! Staying score thought... it... was... ♪"
Getting... farther... and... away...
♬ 200 repeat adds land Wiyu Witchcra... 950th!!
"Staying score thought... it... was... ♪"
Break arrives; students flee without eye contact.
In central plaza, dazed, unfocused eyes, classmate sobs a song—no comfort, they leave.
"Gone... my... rank... where...... Not... my... send-off......"
From afar, Change, Spotty, outer gods, No.1, Void Mask—unable to console master, just quietly weep and watch.
"Everyone lives working hard every day..."
Promotion by grades—now impossible...!! Overwhelming gap... Reality's high wall...!!
"Waaah!!"
Sent Mom a letter saying academy life's great!!! So embarrassing!!!