I just want to give you a teaser for what Kai will learn later on but this technique is what Kai will use in the finals, it's called The Futae no Kiwami it enables one's strength and power to be fully utilized at its maximum output. Though its utilization can be used with all of the body, the use of it through extremities, especially the fist, is often the first part to start with when it is to be studied and mastered.
The Futae no Kiwami's principle aspects come from understanding that all matter bears a level of resistance, and that a single blow's impact is wasted upon meeting this resistance. From this, two blows are to be acted to fully transfer this impact. With the fist, the first blow, using the proximal interphalangeal joints of the hand, meets to absorb the object's initial resistance. Then, with folding the hand immediately to switch over to the proximal phalanx knuckles, delivers the final strike to the weakened object; in addition, the two hits are to be delivered at nearly the same time, with a few milliseconds interval. The result is the complete destruction of the object, which has no more resistance to sustain itself and collapses into dust.
Users
The Futae no Kiwami was created and mastered by Koga Heishin during his time as a sensei for Ayeka, Ryoko, and Tenchi, who Himself needed ten years of his life to completely dominate it. He will agree to teach Kai this technique being he is Kai's grandfather, who will learn the technique in just one week, but only to use Futae no Kiwami with one limb at a time until he ranks up,
Techniques
Kiwami Hazushi (Extremity Release) - A defensive measure used with the Futae no Kiwami. Upon the impact of another's attack, the user delivers a Futae no Kiwami in the opposing direction of that blow onto one's own body, neutralizing and dampening the attack's force by the vibrations sent on the molecular level.
Futae no Kiwami: Rikushin (Mastery of Two Layers: Shockwave) - An advanced measure of the Futae no Kiwami, the user is able to deliver a shockwave of similar impact upon using a tool or weapon and using the Futae no Kiwami onto a surface. Depending on the execution, the attack is seen by Koga to manifest as a grounded radial impact or a surge of force towards the opponent. This technique was initially refered to as Touate
Sanjou no Kiwami (Three Layers Mastery) - A greater form of the Futae no Kiwami in that after when one delivers the first two blows, a third is made by opening the fist to striking with all five fingers.
Futae no Kiwami: Senken (Mastery of Two Layers: Rotating Fist) - A counter measure used with the Futae no Kiwami. As their opponent delivers a blow, the user delivers a Futae no Kiwami but with a twisting motion to parry the opponent's strike and land a blow on the opponent.
Futae no Kiwami: Ushin (Mastery of Two Layers: Full Body) - A defensive measure used with the Futae no Kiwami. The user channels the destructive power of the Futae no Kiwami throughout their entire body, causing anything that comes in contact with them to be destroyed.
Futae no Kiwami: Tsuraneuchi (Mastery of Two Layers: Consecutive Strikes) - The user delivers multiple Futae no Kiwami at a single spot, with rapid consecutive punches.
That's all I wanted to mention right now.
Now onto the story.
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Kai and his teammates stepped into the room as he ran into Naruto's teammates.
" Hello again," Kai said.
" Kai-san," said Naruto with a cheer.
" Hello Kai-Kun," said Sakura with a bow.
" Hn," Sasukè grunted.
Just then a blonde and purple blur tackled Sasuke.
" Sasukè-kun, Oh How I've missed your handsome face," said A girl with Blue eyes and Platinum blonde hair if Kai didn't know who she was he would've wondered what a French beauty was doing here ( for those confused according to certain fandom the appearance of the yamanaka clan is based on European people specifically the French,)
" GET OFF HIM YOU PORKER," Sakura Screeched.
" Oh my miss billboard-brow, what are you doing here," said The blonde.
" Chill out Ino, man this is such a drag," said a boy with spiky hair similar to pineapple leaves.
" Hey shikamaru you're here," Naruto cheered.
" Don't forget about me," said a boy who was a bit on the hefty side.
" Hey it's chouji," said Naruto.
" Friends of your broski," I asked Naruto of course I knew they were his friends they were the only kids who gave a damn about him even after they had their memories wiped the only kid who didn't get their memory wiped was Hinata because she is best girl.
" Yeah shikamaru, choji, and I go waaaay back we met before the first year of the academy," said Naruto.
" 'sup guys I'm Kai Heishin, Nice to meet you," I said.
" Oh we know who you are, the wonder Genin," said Shikamaru and choji.
" More like the lucky bastard who got stuck with the top two beauties of The academy," said A loud wild voice.
" Nice to see you too kiba," said Naruto and Kai in a deadpan chorus.
" Please Naruto-Kun, and Kai-Kun, don't mind kiba," said Hinata with a voice as soft as silk and a shy demeanour.
" Hey cuz did you see Kai whoop neji's teammate earlier," asked Himiko.
" I did but I was distracted by something else," said Hinata.
" Hmm let me guess a certain fishcake caught your eye," Yoshiko teased.
" I told you my name means maelstrom cuz," said Naruto.
" Wait you're telling me your Related to the senju clan," kiba laughed.
" Yeah a couple months back I found out my mother is from the same clan as lady mito hence the name Uzumaki," said Naruto.
" You better watch yourself kiba, the Uzumaki clan was one of the most powerful clans on earth so powerful that they had been attacked by three villages who were afraid of them see the Uzumaki were capable of subduing the tailed beast and a single full blooded Uzumaki is equal in strength to a kage," I replied.
" Well we're lucky cause this losers dad probably sucked," said Kiba.
" Oh yeah jokes on you ass smeller, my father was Minato Namikaze, which is where I got my looks," Naruto bit back.
" Keep dreaming," said Kiba.
Naruto vanished almost instantly and reappeared behind Kiba.

" Are you sure about that latrine licker," Said naruto with a Slasher Grin as he held his Hiraishin Kunai at the nape of kiba's neck.
" When did you," he asked.
" The moment you touched the door handle," said Naruto as he explained, " You see I placed the seal on that door handle and whoever touches it gets the seal put on them," he said with a smirk.
Kiba's eyes widened.
" This was the technique that made my father famous, the Hiraishin No Jutsu and Don't think for a minute you are better than me or my old man or I will send you and your hound crying to your mother with your tail between your legs like a bitch, Do you understand that curr," Naruto said with evident venom in his voice.
Kiba felt the killer Intent of Naruto wash over him he swore he could've seen a mountain sized beast behind Naruto although he couldn't make out what it exactly was.
" Naruto That's-" Sakura was about to reprimand Naruto
" No Sakura Kiba brought it up in himself let Naruto discipline him," said Kai.
" You know what Kiba, I think you need an attitude Adjustment," said Naruto with evident venom.
Kai pulled out a scroll and from out an assortment Of goods alongside a wrapped box " I've got a fly swatter, a wooden spoon, a tree limb, a leather belt, and if you're feeling extreme you can always use the barbie," kai said with a Slasher Grin.
" Of course I always feel extreme," said Naruto.
" What are you gonna do pummel me with a doll," asked Kiba.
" Oh no you got the wrong Barbie in mind," said naruto and Kai.
Naruto opened the box and pulled out a barbwire wrapped baseball bat.
Kiba's eyes widened in shock.

[ It was at this moment Kiba Knew...He fucked up,] said the systems voice.
" Say Hello To Barbie," Said Naruto.
" Uh Kai Kun what is that exactly and why do you two call it Barbie?" Asked Sakura with a pale expression.
" Well Sakura to answer the first question it's a barbed-wire wrapped baseball bat, and to answer the second question it's a simplified name of the weapon," said Kai with a shit eating grin.
" I see so these are the boys my cousins like, Bunch of Trash if you ask me," said Neji.
Kai smiled " eh Naruto you here that that was insult," Kai said.
" Oh no I believe that was a challenge, But I'm beating this dog with a stick right now, so I suggest you handle him," said a Naruto.
" Heh I'd like to see you try, Unfortunately we can't do battle in this crowded classroom," he said.
" Fine I'll see you in the second stage, hammer fodder," I said.
Kiba hid behind Hinata however Hinata just stepped aside after all the mutt did just insult her future father in law, may he rest in peace.
" Well you two clearly got our names on your asses, so we'll see you later I hope you're prepared for a good ass beating because you're going to get one whether you like it or not," said Kai
" And if you're not down with that We've got two words for Ya," Naruto Replied before both Kai and Naruto did a crotch Chop, " Suck It!" Naruto and Kai said in chorus.
" You kids must really have a death wish," said an albino haired Boy.
" And you are?" Asked Naruto.
' One of the biggest assholes in all of anime history second only to Jagi,' thought Kai to himself with a paranoid tone.
" I'm Kabuto Yakishi, And I've been here at least 12 times," he said.
' LIAR your only 19-20 at this time for that to be true you'd have to have been a Genin at age 8 and even then, if you became one at that age you should already be a Jounin by now,' Kai thought.
" Anyway I have knowledge of almost every person here," said Kabuto.
'Further proof your a spy,' Kai said internally.
Kai noticed Yoshiko about to make a move but he put a hand on her shoulder and shook his head she signed to Himiko who nodded.
" Tell me what you know about Kai Heishin," said Sasukè.
" Hmm, Kai Heishin, an odd case, Commonly referred to as the Wonder Genin, About 2 years ago he had low level chakra reserves and control but made up for it with his exceptional swordsmanship he killed 3 kumo-nin, and within 2 months of the first of those two years, he somehow grew stronger, he also killed a Chūnin instructor who tried to attack him who was revealed to be a traitor; he's the disciple of the Misaki clan heir who is married to Tsunadé Senju, and is best friends with Naruto Uzumaki. He's also known for exceptional growth within the past two years within his chakra reserves which have grown from civilian level to high Jōnin level, he also has a special knife made from the Venomous fang of a Kasaka, uses his Clan Kenjutsu, is trained in the misaki clan Taijutsu alongside Naruto Uzumaki and has learned 6 high level Ninjutsu, and two Kinjutsu amongst all these things he has also been stated to have killed an expert level assassin, over 100 men in under a night, and slayed over 500 men alongside Naruto Uzumaki in the land of waves,' said Kabuto.
' Again revealing you're a spy because that's all classified information,' Kai thought.
' System Am I capable of defeating him as I am,' Kai thought.
[ Calculating...As of now you have a 30% chance of defeating Kabuto but it may alter the course of events in the timeline,] said the system.
' Well shit,' Kai thought to himself.
" Silence," said a voice belonging to a rough man With a tanned skin complexion scars over his face and a bandana.
" I'm the proctor for the first phase of the exam and my name is Ibiki Morino, and I'm telling you right now, I have the power to make sure you never take this exam again, Now GET TO YOUR SEATS," He ordered.
" Now this stage of the exam is a written course, You have 45 minutes to answer 9 questions after the 45 minute mark I will give you a tenth question please not that even if you can't finish the first 9 questions you will still be able to pass if you can answer the 10th question," said Ibiki.
" You have one hour, but word of advice do not cheat
Kai was seated in a place that he never thought he would find possible, he was seated between Sakura Haruno and Tenten.
' Great, I'm between the two dick riders, of the two biggest assholes of this current arc, one of them is useful but gets second fiddle and her man is irredeemable until the last chapter, and one is useless and her man has a change of heart after an ass whooping, but dies for character development, this is just great,' Kai thought To Himself.
He noticed that Yoshiko and Himiko were seated next to Ino, and he noticed that Hinata was seated next to Naruto.
He smirked.
' Burai, Morpheus, your up,' Kai thought but don't let people see you.
Burai and Morpheus slipped into Sasuke and Naruto's shadows.
Of course Morpheus slipped into Naruto's Shadow while Burai slipped into Sasuke's and proceeded to send the knowledge to Kai.
Naruto knew about Kai's bloodline as he called it because Kai had shown it to him the night before the battle on the Bridge and explained to him it's abilities so naturally Naruto smirked whenever he was possessed and Naruto began to jot down the answers one answer at a time of course he did it slowly as he didn't want to get caught.
Kai noticed Hinata blushing and smirked as he knew she was secretly stealing glances at Naruto but wasn't trying to look at his paper probably because she was observing the others as well.
Kai had finished his paper right at the halfway mark.
Naruto finished the questions at the same time.
Naruto and Kai then turned their papers over.
A few minutes passed and since then, and Ibiki nodded.
He then eliminated a third of the participants of the exam of course Kai knew this was just a weeding process most of those caught didn't even cheat but that was the goal of the exam but it was also due to how many participants that were used for the exam, fortunately most of them were low level Genin from villages that didn't do much.
Kai felt death glares from two ninjas from the upper left and right he noticed that they were Karui and Omoi.
He just turned to them and smiled at them.
Causing them to grimace and return to their tests.
After the 45 minute mark Ibiki announced that they had the 10th question.
" Alright the tenth question of the exam, you have the choice to answer it or not, please be noted that you can always retake the exam if you don't want to answer this but if you do try and answer it and fail you will never be allowed to become a Chūnin,' said Ibiki.
' Bull! you can become a Chūnin depending on your performance or as a field promotion the whole point of the exam is to evaluate the performance of a ninja and the capability of their leadership,' kai thought.
Most of the group raised their hands and gave up believing it better to rather play it safe than to be sorry.
And Naruto raised his hand but slammed it down on the table.
" Make no mistake, I won't give up no matter what, I will become the heir to the Hokage's name, and if you ain't down with that I've got two words for you, Believe it!" He Shouted.
Everyone was at mixed feelings, Yoshiko, Himiko Hinata and Kai were proud.
Sakura, Tenten, and ino were angry.
Shikamaru, Was annoyed.
Kiba was jealous, Choji just ate his chips, shino just quirked an eyebrow, Sasuke was impressed, and Ibiki just smirked as he knew the kid had the spirit of his parents in him.
" Okay then, for those who haven't given up the tenth question is—That you all passed," he said.

".... WHAT!" The group said in a perfect impression of Li'l John.
Kai just smirked at the reaction he was always entertained at this type of reaction for some reason.
Of course there were some who weren't surprised to be precise they were Kai, Kabuto, and Yoshiko.
Just as the man was about to congratulate them a mysterious ball alongside a banner and Kunai broke through the windows of the classroom as a banner reading number 1 sexiest kunouichi was pinned to the wall with a woman in a full body steel mesh outfit with only a dark orange mini-skirt, and Grey shinguards accompanied her Beige trench coat stood there her wild Violet hair was styled like that of similar fashion to the Nara clan and Iruka of course her forehead protector was also holding her hair back, her Light Brown Pupil-less Eyes and topping it all off was her Snake head pendant.
" Alright you Maggots listen up I'm Anko Mitarashi, the proctor of the next Exam, and if you value your lives you better get your Rears in gear and start Hauling Ass," she said.
'did she even noticed that those two phrases are the same but just with a filter difference,' Everyone thought to themselves.
" Um Excuse me Miss Anko, But I believe you're a bit early we didn't even get to turn on our papers," I said with an innocent reply.
Anko looked at me and smiled, " I see, well I'm glad to see you have good manners Kai-Kun considering you're the son of my hero I wouldn't have been able to forgive myself if lady Setsuna's son were to be a rude punk although I've heard you and that blonde Gaki have told several people to suck it so let me ask you something, Do you even know what that means," she asked Kai.
" Of course i do, but Naruto and I only do it as a taunt or as a joke, we're not degenerates, were just having fun," said Kai with a smirk.
" I see, so you wouldn't mind if I fulfilled that taunt would you," she said.
Kai smirked.
" My Anko-san I knew you were bold but to openly offer to suck off a minor is a new low even for you, guess it's not much to expect from that sanin's disciple," said Kai.
Anko smirked, " You've got guts Gaki, I'll give you that, unfortunately I can't even dream of violating lady Setsuna's Favorite boy," she said.
' Seriously, Who is this lady Setsuna,' Kai thought to himself.
A few minutes later we we're all gathered in the forty fourth training Ground aka: THE FOREST OF DEATH.
A few moments after we got here Anko explained this place to us.
" Okay Gaki's listen up, This is the forty-fourth training Ground Aka the Forest of death, soon you will understand how this place got its name," she said, " and soon you will all experience why this is called the forest of death,"
Naruto huffed in annoyance he put his hands on his hips and began to do his iconic meme dance while mimicking Anko's words.

" Well...looks like we got a smart ass, Gaki's like you are the ones I love the most because when they enter here they squeal like a pig whenever they enter this place," Anko said throwing her Kunai at Naruto but before it even reached its target Naruto was already gone and Anko looked left and right before she realized something was on her head.
" Gee lady, you're right, I do here Ino's mother calling," said Naruto.
This earned a smirk from Sakura and a snarl from Ino.
" Gaki just how did you do that," asked Anko.
Naruto backflipped off of Anko's head and smiled.
" Kai was here about two weeks ago, He said something about hunting a certain snake," Naruto replied.
' it couldn't be, could he be after him as well, No wait he's just a kid,' Anko Thought.
" Anyway the reason I was able to teleport into your head was because you touched the Hiraishin seal on the door handle when you left the academy," said Naruto.
" I see, so not only are you a smart ass, but you've got a good head on your shoulders," she said and then she explained the rules.
Kai just turned her out and prepared for the hunt he had made enough money to be able to purchase a new weapon a knife called the Shinobi Killer of course this was all done without anyone noticing it.
" Alright everyone come and get your scrolls," Said the Woman.
Kai found that his team had the heavens scroll.
Kai smirked at least he wouldn't have to clash with Naruto but now he had two goals the first was to get the heavens scroll the second mission was to kill a certain snake.
" Let's go girls," Kai said to his teammates.
Yoshiko, and Himiko Followed Kai.
Himiko Used her Byakugan to see if any team had the scroll they were looking for and while some did a certain team was heading in their direction the to see if any team had the scroll they were looking for and while some did a certain team was heading in their direction the team of Three Kumo-nin consisting of one boy, and two girls two were dark skinned and one was fair skinned with blonde hair and quite the healthy build for her age.
" Kai we've got company," said Himiko.
" I know," He replied, " You two Go on ahead I'll catch up,"
The two did as they were asked.
Kai drew his new knife, ' if my memory serves me correctly, I have a 75+ attack boost and for every Ninja I face with this blade I'll deal a +25% damage bonus, " welp Let's get busy," said Kai.
Kai had made sure that the girls kept the scroll as the three kumo-nin attacked.
Omoi, Karui, and Samui landed in front of him.
" Oh Lucky Me, I was just about to get ready to practice Some medical Ninjutsu and needed some cadavers, care to Volunteer," said Kai with a Sly Grin.
To be continued.