Weakness

"Oh and you really think you can stop me from completing my task " The Salphuthrite laughs maniacally" hahaha it's quite a ludicrous idea " . 
Kanue however was unfazed "you really shouldn't overestimate yourself like that , after all i was the one who set this up" .
"Set up, you say?" It asked a bit curious. " If i knew someone rather a Salphuthrite would be following me and i just stayed back in school alone, no I'm not stupid and neither are you , you should have known about this" He said expressionless. 
The Salphuthrite smiled deviously " hmmm i was suspecting you'd know and plan all this , guess my suspicion was correct, but then again you do realize you can't possibly defeat me" . Kanue glaze was a bit more intense " that's where you're wrong i might not know anything about you but I'll figure as much as possible in this fight " ,
" Is that so , " It stopped before breathing and continuing" Otigiri Kanue you really are an interesting being " 
Then it's tendril shot out but Kanue weaved to the right , Kanue then brought a sword 
" A sword huh , do you really think that's capable of truly killing me " 
"I'll guess we just have to find out" 
The Salphuthrite used the tendril to try and hit Kanue but he quickly ducked underneath and with a swift clean of the sword Kanue cut it's tendril 
but it immediately regrew , "first observation: Regeneration" Kanue said his voice devoid of emotion
“Kekekekeh” it laughed madly as its tendrils shot towards Kanue at a speed the naked eye couldn’t follow, Kanue jumped over a table and left the room with a quick dash, the Salphuthrite quickly followed him into the hallway 
“So you were just talk after all” It’s voice was dripping with mockery as it set its gaze on him
"Something feels wrong" It thought, usually this was the part where they cowered and beg for their lives but this human looked at it without any regard “I guess you’ve outlived your life” Kanue said, raising his sword towards the Salphuthrite

“Hah, like you can do anything” It scoffed and launched multiple tendrils, in the narrow hallway, there was no place to dodge but Kanue still didn’t look bothered in the least 

The Salphuthrite sped up incredibly fast getting closer to Kanue by second but before it could shot out it's tendril completely, Kanue did a backwards jump in the air "Second observation: extra-ordinary speed " 
Kanue ran incredibly fast and shook his sword straight to the Salphuthrite chest to which the Salphuthrite smiled it grabbed Kanue by the neck with it's "hands" and threw him across the entire hallway 
" Third observation: Extra-ordinary strength" Kanue stood up slowly, The Salphuthrite looked at him curiously "you know I've killed a lot of humans none of them have matched this long against me, so when you lose this , keep in mind , you're strong" 

"My my a compliment from the likes of you , that's oddly interesting" Kanue voice devoid of emotion as usual and his unreadable expression 

"Hehe but for real though when the humans fight me there's always this fear they carry , but from you I don't sense anything at all " 

"That's because i don't fear anything, no rather i don't know what that word means, now enough of the chat let's get back to the fight" Kanue raised up his sword 

Kanue ran over to the Salphuthrite it shot it's tendril out to which Kanue instinctively dodged to the left but the Salphuthrite followed up moving it's tendril to the left at incredible speed but Kanue did a spin turn in the air 
"Shapeshifting , insane Regeneration, extra ordinary strength, extra ordinary speed , all his specs have been pounded into my brain "
Kanue analyzed every move, every reaction. He had accounted for the Salphuthrite’s abilities—but something didn’t add up. If it was truly invincible, it wouldn’t need to fight him like this. It would have finished him already.
There was always a weakness.
The key was figuring it out before he ran out of time.
The Salphuthrite advanced again, its tendrils morphing into razor-sharp blades. Kanue sidestepped, parrying each attack, but with every clash, his sword vibrated harder.
Then he saw it.
For the briefest moment, when its head dodged his blade, its form seemed… tense.
"Hmmm that's strange, he dodged it i don't think I've ever seen him dodge my attacks hmmm is it possible that could be hisWeakness?" Kanue thought to himself while fighting 
"It was the only thing it had consciously moved out of the way. The rest of its body regenerated without concern.That’s it. It must be the head." He thought
Kanue exhaled.
His next move had to be perfect.
The Salphuthrite lunged. Kanue let his sword drop just slightly, feigning an opening.
The Salphuthrite took the bait.
In that split second, as its Tendrils lashed forward, Kanue shifted his grip and twisted.
"A single clean strike. That's all I need" Kanue said 
"What the , he outsmarted me oh no oh no , wait maybe i could try gaslighting him " The Salphuthrite thought in fear 
The Salphuthrite morphed into his teacher" Kanue you don't want to kill me, now do you" it said in Kanue's teacher voice, but Kanue didn't care he went for the kill
For a moment, silence.
Then, its body fell hitting the ground hard
The Salphuthrite’s severed head hit the ground with a dull thud.
Kanue exhaled slowly. "Final observation: Weakness identified."
He stepped forward to confirm the kill—only for his breath to hitch slightly.
Kanue's eyes narrowed

Her lifeless face stared up at him, blood pooling around her severed neck.
Then—
A voice echoed down the hallway.
"Kanue?"
His head snapped toward the entrance.
There, standing frozen in shock, was Ryder.
The scene before him:
His teacher, dead on the ground.
Kanue, sword in hand.
And the undeniable truth that he was the one who killed her.
The weight of the moment settled like lead in the air.
Ryder's expression twisted, his eyes flashing with confusion, betrayal—rage.
"K-Kanue , What… the hell did you do?"