Other Beast Titan...?
"RAAAAAARRRGGGHHHHHH!!" An animalistic roar ring out across Trost, who'd previously thought the battle to already be over...
Bertholdt tries to take this opportunity to run, but Eren and Jean come down on him like a city-sized pallet of bricks. They both simultaneously rush over and slam him into the still-steaming flesh of the Colossal Titan, sending teeth flying as his head slams.
He's knocked unconscious from this, but Eren doesn't stop slamming his face into the flood until Armin and Jean pull him away, both knowing that the information Bertholdt could provide would be instrumental in truly understanding the titans and the world as a whole.
A loud snarl turns all of their attention however, as a man-sized, humanoid wolf with black fur leaps atop the body of the Armoured Titan and begins clawing at its nape, sparks fly as its nails scrape and snap against the armour, but soon enough the wolf finds purchase and peels a plate off of the titan, revealing the flesh underneath.
"Wait, if that thing's like Bertholdt, then there must be someone in its nape too!" Armin exclaims in realisation.
"But what the hell is that wolf-thing in the first place!" Connie shouts, "Look It's wearing the rags of a uniform too! It's probably someone we know!"
"It doesn't matter! We need to stop it before it kills the person inside!"
"... Why though? Why not let it eat?" Eren wonders aloud as the wolf digs further into the titan's flesh. "It's only karma, right?"
"Yes but-"
"AAARRGGHH!!!" Rainer's screams interrupt them as his body is torn from the titan. His eyes were dull but his mouth moved anyway, screaming like a newborn baby as the wolf viciously bit down on his shoulder.
It tears flesh away with ease, and moves onto Rainer's neck, biting down furiously and drinking thickly from the blood his arteries spew.
"T-that's Rainer...?" Eren asks, too shocked to even summon the feelings of betrayal...
"Then... That would make the other titan..." Connie gasps.
"Annie..." Jean spits, looking over to the Female Titan's body where a figure was now fleeing from the steaming hole in its nape. "THERE! SHE'S RUNNING! WE CAN'T LET HER ESCAPE! NOT NOW!" Jean shouts, blasting off towards her and completely ignoring the strange wolf that was devouring Rainer.
"Eren, we need to-" Armin starts but is ignored as Eren follows Jean, intent on not letting a single traitor escape.
"You guys take care of Bertholdt, we'll catch Annie!"
...
"Is it weird that the wolf-thing eats better than us?" Sasha wonders aloud as she finds a comfortable spot to sit and watch Rainer be devoured.
Armin and Connie look at one another with a 'What the fuck did she just say?' look on their faces...
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Once the wolf was finished eating Rainer, it looks up at the sky and sniffs deeply for a moment, before eventually locking eyes with the trio watching it from the Colossal Titan's corpse.
"AWWOOOOOOOOOOO!!!!" it howls before rapidly sprinting towards them, using its claws to dig into the dead titan's flesh and climb its way up.
Armin and Connie begin panicking, but Sasha continues to casually watch, tilting her body to allow the wolf to pass as it charges straight at Bertholdt...
Connie slashes at it with his sword as it passes, cutting a large line into its flesh, but that wound heals right before their eyes...
It ignores them despite Connie's attack and grabs the unconscious soldier before running away, intent on devouring him somewhere out of sight...
"Sasha... What was that!?" Connie asks, unsure why she was so sure it wouldn't eat them...
"Can't you tell when someone's craving something? That wolf wanted Bertholdt and no one else, I could see it in its eyes..." she remarks.
Armin grips his hand with his other to try and stop his trembling, Bertholdt was surely dead and he'd done nothing to try and stop it... He was too much of a coward to even try like Connie... He sighs and looks to the others, "We should go help Eren and Jean, Annie's the only one left with answers."
They nod, "Let's go then."
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"ANNIE! YOU CAN'T RUN!" Eren shouts as he and Jean chase the blonde traitor, Annie using her own 3D manoeuvre gear to try and escape towards the wall.
"RAINER'S ALREADY DEAD! AND BERTHOLDT'S BEEN CAPTURED! STOP NOW OR YOU'LL DIG YOUR GRAVE EVEN DEEPER!"
"What would you two know!?" Annie retorts as she flips over a restaurant balcony and through a terrace.
Eren smashes straight through a bannister in pursuit but doesn't slow at all, the splinters in his flesh only making him more determined to catch her.
Jean on the other hand is far closer to catching her, only a couple of meters from being able to grab her.
"I PROMISE! GIVE US ANSWERS AND WE'LL PUT IN A GOOD WORD FOR YOU! ANNIE!"
"GO TO HEL-" she starts to shout back but pauses as she spots something behind them... A blood-covered humanoid wolf sprinting through the street at speeds far greater than their 3D manoeuvre gear could ever match. "WHAT THE-AAAAAGHHHHK!"
The wolf leaps up high and easily snatches her out of the air, immediately beginning to tear the unfortunate blonde to pieces. Her forearm crunches loudly as it bites it, claws dig deep into her chest and pierce a lung, and the flesh on her face gets half-torn off from a relatively small nip from the creature.
Eren and Jean land on the ground next to the scene just as the wolf tears Annie's jugular out and continues on to chew on her spine. After that, it thrusts a claw into her chest, pulls out her still beating heart, and devours it in front of them...
"W-what creature are you..." Jean utters in shock.
"One that's on our side, aren't you?" Eren asks as the wolf turns towards them, blood dripping from its maw... It raises its head up and releases a long howl before passing out onto its back, its body rapidly shrinking until a naked Mikasa is all that's left.
...
"What the fuck!?" Jean exclaims.
"Mikasa...?" Eren confusedly mutters, his mind blown by just about everything that'd happened in Trost thus far. Unbeknownst to him, he didn't even know half of it.