Kuro experienced the feeling of destroying and the feeling of strength over other today.
He was still in the training ground, practicing but even after getting used to the power, he did not develop anything, he did not consider himself as a genius but
he switched between the energies but when he tried to mix both, Ki would swallow the Chakra as if it was nothing.
Kuro was already content with the power he received, but he was in no sense invisible, if someone surprised attacked him he would die instantly as an infant would die if he was attacked.
And thinking this, Kuro had a thought, why not strength his body, his eyes and his limbs with Ki?
And especially his brain, to react fast to attacks.
And to not mess this up Kuro used little ki as possible, as in not to fry his brain or to explode his limbs accidentally, as it would be very stupid.
Slowly he released the Ki from his organ and pushed it towards his limbs, finding no problems, no strain but strength he pushed the Ki to his whole body, just below the Jaw.
Not to his eyes and not to his brain.
Not long after, the control suddenly dropped and his fingers curled backward and they all broken in a twisted manner.
The pain hit him, he brought his other hand to his mouth and clenched his teeth's and beared with pain.
He broke many bones in his life as a kid and as a teenager, and this was not something new.
But to say the least it was the first time for his hand to have broken all his fingers at the same time.
He wanted to scream but in his whole life, in his his society the person who screamed from pain or even from a surprise scare was not thought of as a man.
And in his childhood his cousins would smack each other or punch each other, including him to know who was the stronger one.
To say the least he was the one who won everytime.
And due to this he never cried from pain nor from breaking his bones, it would be grunts or a flat serious face.
One time he remembered he dislocated his arm and went to his mother to show his arm, and when he showed her how it twisted in an unnatural way, she almost passed out.
Kuro stopped the flow of his Ki and instead he used his Chakra to fix his fingers.
First he placed them in their natural places and used Chakra based healing, to heal his fingers.
The healing technique was taught by the academy, it was given to everyone, and only a few could use the technique and Kuro was open of them.
In the academy they were taught everything to survive, most of the teachings were focused on strategy, how to set up traps, Kunai throwing and taijutsu.
Little was for ninjutsu, but genjutsu and clone jutsu were also taught.
It was a simple system, everyone started on zero, the academy introduced ninjutsu and every variants jutsu (taijutsu and genjutsu).
Those proficient were separated from the non proficient ones and those who failed were separated from the non proficient ones but were barely able to use.
It was a separation of class A, B, C, D, F.
A with the most potential and F with lowest potential.
Kuro and Minato were in class A.
Though even if you were in class A, that does not mean that you are able to use all the ninjutsu, some could use taijutsu very well but some could not use ninjutsu at all or a little and vice versa.