· When Kai was four years old was when the Arcadian magic manifested in him, his magic turned out to be somewhat unstable so his parents used the only material that could suppress the Arcadian magic, it's a strange material called Vengestone, and it's the only mineral capable of suppressing Arcadian magic, it is rare and almost impossible to find, but only Ray and Maya were able to obtain some of that material to hide their children's powers in case they get out of control from the public. Ray and Maya were able to teach Kai some control of his magic, but only the basics, however Kai taught himself to control his power during his growth and thanks to Garmadon. He stopped wearing the bracelet after his parents disappeared.

· Before their home was attacked, Kai and his family lived in the blacksmith shop that Ray built to be able to settle underground and live quietly, it was small but cozy to support the four of them. Every night that Nya cried Kai would leave his room and climb Nya's crib so he could be with her all night and not leave her alone.

· Kai knew Garmadon for as long as they can remember, also Wu and Misako, but he didn't see them much. Garmadon was his father's best friend and only Garmadon knew that Kai and Nya had magic after their parents disappeared, but what Garmadon didn't know was that Kai and Nya were descendants of First Ones.

· Kai may have heard the stories of his parents about his offspring and about the First Kingdom, but those memories made Kai think that they were just children's stories and that nothing was serious, not even Kai told Garmadon about these stories when he began to training him along with Nya, Kai told Nya few stories, and sang her the lullaby her mother sang to her, but she told the stories as if they were just fairy tales.

· Although they do not know it, only Kai and Nya can read the language of the First Ones, a quality that the First Ones inherited to their offspring so that they could decipher the symbols throughout the planet, they are even able to understand the creatures that have Arcadia in their interior and only the First have that ability. And that's why after everyone meets Kai and Nya manage to help Zane, Cole and Jay in their research on magic and to decipher the symbols they discover during their journey.

· After Kai's eye was severely injured by one of the royal guards, Nya, still a baby, managed to awaken her power to heal him, which surprised Kai and it was lucky that no one had seen her power in the commotion. But after that Kai gave him his Vengestone bracelet so that he wouldn't reveal himself so easily to others, and he noticed that his sister's powers were a blue color associated with water while his were a red color associated with fire. .

· A year after the coup, Kai managed to improve his control over his powers thanks to the lessons of his parents and Garmadon, at first he used them as a game, he jumped on any building and could burn any post he wanted, but Garmadon forbade him. use his powers in public and that he only use them if necessary, because if they found out about his powers he would be wanted and they would want to seize him.

· He normally spent his time taking care of Nya when she was a baby, staying in the lair and doing all the chores around her house, when Nya turned five Kai eventually went on missions with other rebels while she stayed in the guard or with Garmadon. But sometimes he would leave her with Ronin or old Mystake, a wise old woman and informer throughout the underground, since she could talk to some creatures that served as her informants, she was also a descendant of the First Ones. In addition, Mystake was also the one who took care of Kai and Nya when they were little, it was like their personal nanny.

· When Kai and Nya met Lloyd at first he was a bit uncomfortable when Garmadon told him that Lloyd would be like his second younger brother, Kai didn't see him much but every time they visited him the little baby always played with them, and he didn't let go for anything From the world of Kai's spiky hairs and liked to play with his powers, Kai and Nya entertained Lloyd with figures created from his powers. They didn't see Lloyd much, but whenever they visited Kai and Nya they always played with him. The only one who didn't know that they were going with Misako was Morro, since everything was kept secret.

· Garmadon trained Kai and Nya well, thanks to him, the two brothers managed to survive the dangers of the underground, in addition, thanks to Ronin they managed to be great thieves and excellent athletes and mechanics. Kai even learned to fight thanks to Garmadon and Ronin, he was even able to build his own weapons, he is good at using swords and his fists, but he is not so good at target practice, that talent was only inherited from his sister. Also, he had to carry Nya on his back every time they jumped over the roofs.

· Kai is very grateful to Garmadon for becoming his guardian, and has always enjoyed spending time with him, whether it's training, on quests, or at the bar. Kai even assists in the combat training of new members in the rebellion, and makes sure their jobs are not interrupted by the royal guard, the police, or other troublemakers underground.

· Thanks to the missions of Ronin related to the city of Ninjago Kai improved his theft and athletic skills, he has always liked to climb the tall towers of Ninjago and jump from them to feel the incredible sense of freedom when he felt that he could fly through the clouds. Geez, something I taught Nya, but it started with small towers and where there were better landing areas, using his hoverbike is the best thing Kai can enjoy, even when running from the police or guards by Nya's side.

· Kai taught Nya everything about how to defend herself, he was also very surprised to see how Nya was a good inventor and marksman, he also doesn't like when some policemen and royal guards interrogate them, he doesn't like the idea that Nya grows up with a horrible image of him being subdued by men of the law, he also likes to see how Nya spends time with Garmadon, but seeing that Mystake gives her more prizes makes him feel a little jealous.

· He is very surprised with Nya's ability on science and machines, he also congratulates her a lot for the training circuit that she herself created, in addition, several of her tools were very useful for missions and robberies, she almost even finds it hard to believe that Nya created an android out of the garbage, and he is relieved to see that Nya knows how to master her powers well, it helps her a lot to master them for combat, but Nya sometimes prefers to use them to heal wounds and give life to various machines, which sometimes they are able to feel and have some consciousness.

· Not many times Kai and Nya agree, they have their typical sibling fights and sometimes joke around with each other, they even play their own games and even Kai lets Nya sleep in his bed as an old habit, he doesn't tell her much about his aes but Kai only talks to her about them if she wants or asks. Sometimes Kai takes Nya to the surface to see the stars.

· After the events with Tyrrant, the explosion and about his wrongful imprisonment, Kai thought that his life ended after separating from Nya and losing Garmadon, it even affected him too much when he lost his right arm and had numerous critical injuries, now only that What he was looking for was revenge against Tyrrant, he swore that if he ever got out of prison he would look for Tyrrant and his men, but he also decided to find Nya if she was still alive.

· After Nya built Echo Kai, he implanted combat programming into it to protect Nya in case he wasn't around. She even helped Nya fix Echo's fallen parts.

· During his time in prison Kai managed to make the inmates fear him so they wouldn't mess with him even due to his condition. He refined his fighting and stealing skills while being held captive while also studying the other prisoners and learning both their abilities and weaknesses. He even practiced his powers on the sly, as long as they didn't put his Vengestone chains on him, which is the metal they use in prison for cells and shackles.

· At first several inmates tried to intimidate Kai but all of them ended up in the infirmary when Kai arrived at the prison. Kai even forced an inmate to draw some tattoos for him. Kai even made it clear to the guards not to mess with him, as he broke one of their fingers when they tried to intimidate him. Despite having only one arm and a half-blind eye, Kai still knows how to fight very well, and over time his fighting skills have increased.

· Kai didn't sleep well after he went to prison, he hasn't stopped having horrible nightmares about the event with Tyrrant, he took it out on the wall and he didn't care that his only arm was hurt. He even forced each prisoner into information on Tyrrant's whereabouts, but not many were helpful.

· Almost every day he tried to escape and study the weak points of the prison, but almost all his plans failed, the only way he knew to get out was for someone from the outside to free him. He didn't even complain when he did prison work.

· Kai was known by the prisoners as the Red Shogun, and his tattoos symbolize various things, his identification number is tattooed on his neck, and he has the symbol of the resistance, the shield of the underground, the symbol of fire and the drawing of a dragon with fire around.

· He likes underground junk food and alcoholic drinks and sweets as that was what they always served in prison, he got used to the bad taste of food when he was just put in prison.