Kuro knew that if he doesn't open his seal he would ultimately lose against his opponent but if he or Shiro opens their seal then their body would suffer harm.
Their bodies were improvised by their sensei but this cause their body to go a drastic change and only the seal would be able to stop them from losing themselves.
For example he was compatible with fire element so his body was fused with a Legendary Grade dark and fire type monster to improve his strength.
He would become like a werewolf and because of the monster spirit in his body he would need to exercise caution if not he would go out of control.
But his opponent in front of him could take him even if his seal was opened heck he even had less than 50% chance of winning even if he opens his seal thankfully for him he was of the fire element if not he would surely lose.
Also after he returned back to his normal form he would be weakened for at least day and that is only if he stayed in his unsealed for a short time if he took any longer then his weak phase would be longer.
With a shout dark energy burst out of is body as an illusionary figure of a spider with flaming eight legs appeared.
Then Kuro started changing as suddenly four spider legs grew out from his body while his legs and arms were set ablaze.
He then spoke in a hoarse voice "Kinji rareta tekunikku: Akuma no henka" (Forbidden Technique: Demonic Change).
Upon seeing the changes that happened to his opponent the Metal God Technique practitioner was not scared on the contrary excitement could be seen in his eyes.
He then let's out a battle cry as he also started to go a change as his skin started becoming steel and after a while he turned into an iron man.
His skin has some kind of dark tattoos with complex structure that looks like runes.
With his strength increasing in a great level the Metal God Technique practitioner immediately charged towards Kuro with his fist raised high.
Kuro was already having a hard time reigning himself and even with his incredibly tough will he was still overwhelmed by the emotion of bloodthirst.
With his opponent strength that causes the monster part of him to feel threatened what's more his opponent was getting closer.
Screech! He lets out a very uncomfortable shriek before losing control as he lunged himself towards his opponent.
The Metal God Technique practitioner did not care about the lunging berserk Kuro and punched out.
Bam! Together with his vital force and metalqi he punched Kuro's face causing him to stumble backwards.
Just as Kuro was about to raise his head he saw a foot descending towards his head.
Bam! His head was planted on the stage the spiritual sense barrier started cracking but ultimately recovered immediately.
The Metal God Technique practitioner used two Metal God Technique the Mountain Boring Punch and Descending Destructive Blow.
These two skills from the Metal God Technique is lethal the only reason that Kuro's head did not burst because his opponent wanted to fight a thrilling battle so he did not use much of his metal qi and vital force.
Just as the Metal God Technique practitioner wanted to continue he saw that Kuro was unmoving just as he thought his opponent have fainted a pillar of flame burst out of Kuro's body.
Kuro then hurriedly created a distance between the two of them.
Kuro have returned back to his usual calm self the monster side of him was beaten to the point it relinquished the control of his body back to him.
His opponent did not hesitate and charge towards the flames as his vital force cover his whole body deflecting the fire energy.
Kuro spread out his two palms as took out his gloves and started shooting out spiderweb out of his fingertips.
The Metal God Technique practitioner spread his arms before clapping them.
Third Skill of the Metal God Technique: Metal Shock.
Bang! A loud noice was heard as the two hands collided with each other as a shockwave attack repelled all the webs and was still flying towards Kuro.
Kuro used the four spider legs on his back to cover himself as the flames that was attached on them started burning much more brightly.
Bam! As he received the attack he was pushed backwards.
Just as the Metal God Technique practitioner was about to charge he felt extreme danger and quickly rolled to the side.
"Katon: Karyū no hōkō!" (Fire Style: Fire Dragon Roar).
As the flaming dragon was formed it lets out a roar.
The appearance of the flame dragon has changed this time it was bigger and a hint of dark malicious energy is within it.
As the fire dragon dashed towards the Metal God Technique practitioner the temperature in the stage rises.
Boom! As the dragon slams itself at the Metal God Technique practitioner a loud explosion occured as the people near them was thrown away.
Kuro then used the hairs on the four spider legs on his back to sense if they managed to hit his opponent.
He then found nothing in front of him causing him to be alarmed but just as he was about to flee it was too late as a pair of arms appeared underneath him and grabs his ankles.
With a pull he was slammed into the stage the Metal God Technique practitioner leaps up from underneath the stage as the spiritual sense barrier once again enveloped the spot where he crawled out to.
The four spider legs started attacking him as Kuro was laying on the stage but with his four spider legs he was able to retaliate.
The Metal God Technique practitioner grabs the two spider legs but the other two stabs his body.
But they didn't pierced through as sparks started to appear as the two spider legs tried to pierce through his skin.
The Metal God Technique practitioner pulled Kuro lifting him up before smashing him once again.
Bam! As Kuro was slammed he shot a couple of webs towards his enemy.
The Metal God Technique practitioner was shot but the webs did not do any harm but his expression still changed as he used his vital energy to once again used the Metal God Technique first skill Mountain Boring Punch.
This time he wasn't holding back as the force cause the wind to break.
Bam! Kuro took the blunt and flew towards the wall he was so fast that the audience only saw a blur.
Boom! As Kuro was slammed into the wall the arena shook just as everyone thought that he was eliminated the Metal God Technique practitioner grab something that looks invincible and pulled.
Kuro once again flew towards the Metal God Technique practitioner.
The audience were shocked that Kuro was still conscious he then stop.
He cut off his strings that was attached to his opponent.
Before he was slammed into the wall he pulled hard at his string and lessen his speed for the last few seconds he then used his four spider legs to block him from truly smashing into the wall.
He couldn't help but frown even though he reduced the force he still took a powerful blow and his body was still reeling in shock.
Thankfully he had a powerful regenerative ability from his monster side but he still need time to recover that is something his opponent wouldn't give it to him.
And just like what had had thought his opponent quickly charged towards him but suddenly a person stops him.
It was Shiro and just like Kuro he also unleashed his seal and used their secret technique the Kinji rareta tekunikku: Akuma no henka (Forbidden Technique: Demonic Change).
Unlike Kuro he looks like a human shark he had a fin on his back and gills on his neck but he could breath in land.
With a stomp he slashed out as the Metal God Technique practitioner punched out.
Bang! Shiro was thrown backwards as he slams into the wall.
Kuro on the other hand shook his head as he knew what had happened Shiro lost control of himself.
After all Shiro is the more sharp of them two while he was somewhat a hotheaded person.
According to Shiro's usual personality he would never fought a practitioner of Metal God Technique head on considering their almost godlike strength.
As Shiro shook his head he recovered from his berserk but their opponent was already in front of him sending a punch on his face.
Suddenly the Metal God Technique practitioner stops as he quickly retreated as numerous flaming ravens went after him.
Kuro heaved a sigh he manage to unleash his technique right on time.
Katon: Hyaku Enjō Watarigarasu (Fire Style: Hundred Flaming Ravens).
Shiro then used this chance to ran towards him as their opponent was still busy dealing with the ravens.