I'm always in awe at the transformative power of second chances, to give someone another try at life can be fundamentally healing and rewarding for both parties. Forgiveness is integral to KNY as a story so second chances are important and almost always are portrayed positively.
like in the case of Hakuji who was saved by Keizo's love and capacity to see and treat him as more than a criminal, admirably Keizo met the boy and right away decided that there was something within him that was worth saving, so he took him in and entrusted him with his precious daughter, allowing Hakuji to flourish and embrace his gentle and principled personality. His story is a good example of how punishment and alienation as tempting as they maybe can be extremely destructive and short-sighted, because for Hakuji it was love and positive affirmations that pushed him to be a better version of himself. If Hakuji was dismissed by his teacher then none of the goodness that three experienced would have happened. Keizo poured hope into him and in exchange he became a loyal student, a son and a great support for Koyuki, he loved and saved her until the last moment. If Keizo did not give Hakuji a chance to redeem himself, his daughter would have never found love and he would have never had a son to carry his legacy.
It goes beyond individuality though, because the forgiveness that Yoriichi Tsugukini showed to lady Tamayo altered the entirety of the story. Yoriichi could have easily killed the demon the day he came across her, he would not have been wrong either because Tamayo had made plenty of mistakes up till that point, so killing her would have been justified, but he saw something in her that day: a desperation for Muzan's downfall even if it meant her own death. That really convinced Yoriichi of her earnest desire to change and in turn his belief in her encouraged her to transform herself. After their encounter she started feeding on animals, evading Muzan, and helping humans. Letting her go was the indirect cause behind her encounter with the Kamados, and creating an alliance which helped in creating the poisons that helped in defeating Muzan.
It is the same with Shinjuro and his sons. It was Kyojuro's non-stop belief in his father and his recovery that affected Shinjuro the most. We saw the impact of Shinjuro coming to terms with the devastating loss of his eldest son and his transformation in order for him to become (or go back to) the hero his son always saw in him. Kyojuro worked hard and kept up hope, he saw a better path for his father and made sure that his last words reflected that. Those words became a code and a promise Shinjuro followed to overcome his alcoholism. It was not just those words that guided him but Senjuro's forgiveness as well. We do not witness that forgiveness unfold but it was implied by the end of the story that the youngest son decided to turn a new page and give his dad a chance to redeem himself, which ultimately benefited the both of them.
Finally, one of my favorite examples: Tengen and Kagaya. To Tengen and to the world, he is a killer, Kagaya could have seen him as such and nothing more, instead he gave him a chance to make up for his past mistakes, and never judged him. Kagaya gave him a place within the Corps and complemented his willingness to fight for the innocent, going against everything he was taught since childhood. He accepted and praised Tengen instead of rejecting him, because of that he was able to help with defeating upper moon six and setting off a chain reaction that rippled throughout the story. The defeat of Muzan and the eradication of demons is a feat that would not have been possible without every player and Tengen played a pivotal role.
So, whether it is Keizo giving Hakuji a second chance at life and inadvertently giving his daughter a second chance at life as well, or Yoriichi letting his mercy triumph over his judgment which allowed Tamayo to live and create a poison that stopped Muzan, or Kyojuro and Senjuro's forgiveness allowing their father to heal and return to his old self and to them, or Tengen being allowed to atone instead of being disregard and written off, second chances have the power to transform and better our lives and the world as a whole.
