Throughout the Star Wars sequel trilogy, Kylo Ren had an unstable lightsaber he never bothered to fix - but why? Debuting in J.J. Abrams' Star Wars: The Force Awakens, the character was initially introduced to be the primary villain of this new age of the franchise. Born Ben Solo, Kylo Ren was the son of Han Solo and Leia Organa. Given his familial connection, he, too, was strong with the Force and was one of Luke Skywalker's students as he attempted to rebuild the Jedi Order. A series of misunderstandings and bad calls, exacerbated by Palpatine's corruption, led to Ben embracing the dark side, becoming a leader of the First Order and Supreme Leader Snoke's right-hand man as Kylo Ren.
As Darth Vader's grandson, Ben was enamored by his grandfather. Much of his dark aesthetic was inspired by Vader, including the cape and Kylo's Vader's mask and Ben was motivated to follow in his footsteps. Given this, it's curious why he never fixed his lightsaber's unstable blade to emulate Darth Vader's. Aside from the shaky blade, its cracked kyber crystal needed the lateral vents on either side of the handle to redirect extra heat from the gem. As it turns out, Ben Solo, a.k.a. Kylo Ren, actually liked its "volatile nature" as stated by The Rise of Skywalker Visual Dictionary.
This particular decision makes his lightsaber the only thing in his ensemble that visually represents the real him. Just like his weapon, Kylo Ren was extremely erratic, emotionally immature and triggered quite easily. While the character was adamant about finishing what his grandfather started, he was torn between light and dark, similar to the cracked kyber crystal split in half in his lightsaber. Killing his own father in The Force Awakens was an attempt to kill the good part of him forever and commit fully to the dark side. Ultimately, between his mom's last-ditch effort to reach out to him and his dad's appearance before him in Star Wars: The Rise of Skywalker, he was convinced that it wasn't too late to be redeemed and come back to the light.
Kylo Ren's refusal to fix his lightsaber further supports the notion that his decision to join the First Order and antagonize his family was a plea for attention and an act of rebellion. The book properly explained how Palpatine was able to turn Kylo against the Skywalkers from Ben Solo into Kylo Ren, something that the films failed to do. It's not that he didn't have a tendency to darkness in him already, but Palpatine exploited it. According to the book, Ben was already feeling sad and lonely; Han was regularly away on long runs while Leia was occupied with her Senatorial duties. Ben turned to Luke for guidance, but his uncle's betrayal only further motivated him to seek the dark side, instead.
It's an understatement to say the Star Wars sequels had a lot of wasted potential but arguably none more so than Kylo Ren. Disney had a great actor in Adam Driver in the role, with the foundations of a great character already in place. Unfortunately, the Star Wars sequel trilogy somewhat failed to expand upon that, resulting in a less compelling villain compared to those who came before him.
