Summary
- Kylo Ren's character arc in the Star Wars sequel trilogy closely mirrors Darth Vader's, but he was never a Sith like his grandfather.
- The only Sith act that Kylo Ren committed was when he betrayed Supreme Leader Snoke, following the Sith Rule of Two.
- Despite Kylo Ren's many dark deeds, few of them aligned with the Sith religion's rules, proving that he was not meant to be a true Sith.
Kylo Ren only ever committed one act that truly exemplified the Sith in the Star Wars sequel trilogy. As the main antagonist of the Star Wars sequel movies, Kylo Ren was set up as Darth Vader’s heir, not just because of his familial ties to Star Wars’ most iconic character, but because of his role within the narrative, as well. He was the powerful dark side Force-user that hindered the Resistance and its heroes at every turn, the one who tortured and hurt the sequel trilogy’s protagonists every chance he got, until he finally found his way back to the light in Star Wars: The Rise of Skywalker and redeemed himself by saving Rey's life.
Despite Kylo’s character arc sharing so many parallels with Darth Vader’s, Kylo Ren never committed as many atrocities that could qualify as pure Sith. In fact, only one act ever truly qualified as a Sith act, no matter how hard he may have tried to prove himself to Snoke, and Palpatine, by extension, during the Star Wars sequel trilogy. This is one of the reasons why Kylo Ren was never an actual Sith – instead, he was a dark side adept.
Kylo Ren Followed The Rule Of Two When He Betrayed Supreme Leader Snoke 
The Sith Rule of Two is simple – there can only be one master and one apprentice. According to Star Wars creator George Lucas, the Sith Rule of Two was implemented because it was the only way to maintain order within the Sith religion. This was because the Sith’s greed and lust for power always drove them to kill one another, weakening their overall standing in the galaxy. However, this rule also drives Sith apprentices to kill their masters to usurp their place in the hierarchy, a vicious cycle that has happened for millennia. This is, incidentally, exactly what Kylo Ren did to Supreme Leader Snoke.
In Star Wars: The Last Jedi, Kylo Ren kills Snoke at a pivotal moment. Snoke had ordered Kylo to kill Rey, but instead, Kylo decided to kill Snoke, asking Rey to rule the galaxy with him afterward. And yet, despite this being a classic Sith move, even this wasn’t a truly Sith act, as Snoke himself wasn’t an actual Sith. He was Palpatine’s genetic creation, one who hadn’t genuinely mastered the ways of the Sith and, thus, he was not an actual Sith Lord. Nevertheless, Kylo killing the one he believed was his master was undeniably in keeping with Sith tradition.
Nothing Else Kylo Ren Did Was In Accordance With The Sith 
Despite many dark deeds, nothing else Kylo Ren ever did was truly in accordance with the Sith religion’s rules. Kylo's patricide didn’t count, either. Though having Kylo murder Han Solo was meant to bring Kylo over to the dark side once and for all and reflect an ancient Sith ritual, Han’s selfless sacrifice negated Kylo’s actions. Han allowed his son to kill him in the hopes that Ben Solo would one day return from the dark side. Though it was an undeniably dark deed, it was never truly Kylo’s own decision, and as such, can’t be considered a Sith act.
