About Kinich tragic and heartbreaking backstory
I think people deserve to know his backstory, because everything is locked behind his Friendship lvls. In Chasca's Story Quest we could learn some things about her past when she was a child, but Kinich didn't have a chance to tell us about it at all. His childhood traumas are possible reason why he's unaffected by Ajaw's screams and only silences him when Ajaw bothers others.
I think some people can identify with his story, which makes it all the more worth reading. In my opinion, Mihoyo did a very good job of presenting in his story how trauma affects a child and how this trauma is reflected in adulthood.
TW: Alcohol, domestic violence, death
Alcoholic father, death and loneliness
In Friendship Lvl 1 we can learn that Kinich lived with his mother and father, who was a gambler and alcoholic (he got drunk when he didn't earn anything at work). His mother and father argued, there were fights (his father beat his mother). One night his mother sneaked out and left without making the slightest noise, leaving little Kinich. She left him perhaps out of fear that her husband would chase her to the ends of the earth otherwise.
Kinich doesn't remember if he even said goodbye to his mother, but despite this he skillfully took over her household chores, farm work, hunting and... beatings from his father. Kinich was constantly trying to escape from home, as he grew older he became more flexible, which made it difficult for his father to catch him.
On his seventh birthday he asked his father for the first time if he had any news about his mother. His father then became furious, started chasing him, tired from a hangover from constant drinking. His body wasn't as strong as it used to be because of the alcohol, so when the was chasing Kinich, he lost his balance and accidentally fell off the cliff.
Kinich looked at the fallen man, it took him a moment to realize what had happened. He felt numb, dizzy, sour. Only then did he feel the tears and, holding them back, pulled the stiff body out with the grappling hook that belonged to his father. As a small boy, now he flew past tree branches, the wind whistling in his ears, holding the dead body of his own father in order to put him back inside the house... Kinich finally had "freedom," but that freedom turned out to be loneliness.
Sad lesson about the value of money as a 7 year old living alone
In Friendship Lvl 2 it is written that after his parents left, Kinich lived alone in the mountains as a child. He gathered food, earned a living and refused help from others. He was still only 7-8 years old. Such a life made Kinich understand that nothing is free and mora is the most important. The only person from the clan who managed to help Kinich was Elder Leik of the Scions of the Canopy, who was responsible for the children's education at the time. He convinced Kinich after many attempts to attend school, because he was worried about him and in return Kinich acted as a courier for him as payment.
Kinich walked barefoot, wore an ash-stained headband, a thick, handmade linen shirt and a skirt made of animal skin, which made him look like a wild child. When Elder Leik taught the children during the class about being a hero, Kinich didn't understand why someone would sacrifice themselves for nothing. He stated that if he became a hero, he expected mora as a reward. This is due to the traumas Kinich had living alone, and even when he had parents and they lived in poverty. The children who were sitting next to him laughed at Kinich. One of them said:
"Why don't you go back and swing from the trees, you selfish mud monkey?"
The naughty children literally threw Kinich out the door by force, but he took advantage of this to leave and drop out of school altogether. According to Kinich, these children were just noisy brats. Kinich was twice as smart for his age. When they praised heroes, it seemed to them that they were becoming heroes themselves or their companions, but such false praise would not teach them how to fill their bellies. And as soon as school ended, each of them would have to go home and be fed by their mother.
In later years, Kinich became a popular courier in the clan, some of the elders of the clan were not positive about him. Only Elder Leik supported him. Despite this, Kinich did his thing, earned mora as a courier and became a Saurian Hunter.
Kinich has already died once (literally). How death and fighting with his comrades changed his view of being a hero
Kinich found Ajaw and made a pact with him, which was that Kinich would finally get Ajaw out of his confinement and show him the sun/world in exchange for power. And when Kinich died, Ajaw would take over his body. Kinich took part in the Night Warden War. The power of Abyss caused some monsters to take the form of loved ones, including Kinich's mother. However, Kinich didn't give up and even killed that monster.
Abyss was so strong that there was no end to the monsters. Kinich was the only warrior standing, but critically wounded. Ajaw promised him then that if he died, he would kill all the monsters and avenge all the warriors. Kinich laughed and with the last of his strength defeated a couple of monsters, when suddenly his chest was pierced through from behind. Crimson drops snaked on the ground behind him, their trail being his finale. Finally, his body fell to his knees. He could do nothing more.
Kinich, the last of the Night Guardian warriors, was killed.
Then, according to the contract, Ajaw possessed Kinich's body and threw himself at the monsters. However, Ajaw noticed that a glowing gem appeared in the hole on Kinich's chest - a vision. After the fight, Kinich woke up in the stadium, alive, along with the others. He managed to survive and received a vision. That night, when he received a new life, Kinich tossed from side to side on the bed, running his fingers over the emerald vision.
Then, completely unexpectedly, it dawned on him that he had strayed from his original goal. He had set out to fight to become a hero for the good of the mora, but now he was fighting for something much more valuable. For his companions, his homeland, the laughter and joy of people... He didn't know when this process began. In fact, the seeds of change could have been sown much earlier - during lessons from Elder Leik in childhood. Then he remembered Elder's words in class about heroes:
We remember our heroes not only for their strength, but also for their spirit of sacrifice... This is the virtue inherent in heroes... Because it is the foundation of noble character, and it is what makes a hero a hero.
He has heard screams and arguments since he was born, it's very likely that this is why he doesn't get angry at Ajaw when he shouts and complains loudly. He only silences him when Ajaw annoys other people. His opinion of the mora and what it means to him is a result of childhood traumas. When he was 7, he saw the death of his own father, who beat him for years and who caused his mother to leave. Despite the fact that he probably hated his father, he still took his body and flew home. All when he was 7. My humble theory is that his drastic childhood is what gave him such a blank, unblinking gaze (like Childe). Because he had to manage on his own from such a young age, he has also learned to work solo - he doesn't work with anyone, he prefers to work alone.