In Star Wars: The Rise of Skywalker, the former Stormtrooper turned Resistance fighter Finn strikes a killing blow against both the Empire and the First Order. Finn's journey began back in 2015 with the release of Star Wars: The Force Awakens, in which he defects from the ranks of the First Order after witnessing the slaughter of an entire innocent village. Initially, his first instinct is survival, but upon meeting other heroes such as Rey and Poe Dameron, Finn assists Han Solo and the Resistance in destroying the planet-busting Starkiller Base.
This evolution is expanded in Star Wars: The Last Jedi, where starship engineer Rose Tico opens Finn's eyes to the injustices perpetuated throughout the galaxy as a result of the conflict between the First Order and the Resistance, forever bonding him to the ideals of the Resistance.
Star Wars: The Rise of Skywalker finds the Resistance in dire straits that they've faced throughout the entire Sequel Trilogy, with the shocking return of Emperor Palpatine and the rise of the Sith Eternal cult further complicating their war with the First Order. To make matters worse, Palpatine attempts to seduce Kylo Ren by gifting him an armada of Star Destroyers, made in secret by the Sith Eternal cult - each one equipped with a planet-destroying superweapon.
While the film ends with the Resistance triumphing over the First Order and defeating the Empire once and for all, there have been numerous story points filled in by supplemental material, most notably the movie's junior novelization, which confirms Finn is the one who technically destroys Palpatine's entire Star Destroyer armada, crippling the enemy's offensive.
Initially, the Resistance deployed a ground invasion squad led by Finn to find a navigation tower on the surface of Exegol that, when destroyed, would cripple communications and navigation connectivity among the First Order fleet. However, Palpatine loyalist General Pryde was one step ahead of them, switching the signal from the tower to his personal command ship, which forced the Resistance to redirect their plans, so Finn and the Resistance troops were dropped directly onto the surface of Pryde's Star Destroyer.
While the movie shows the aftermath of the Battle of Exegol, it doesn't go into express detail about how Finn's attack simultaneously crippled the Final Order fleet and other First Order star destroyers across the galaxy. The junior novelization, however, reveals Pryde's ship was connected to all the First Order ships, bringing them down, too.
"This is the command ship," Jannah said. "We take it down, com-scan goes down."
"Affecting every Star Destroyer in the galaxy," Finn said."
This addition adds a new context to Finn's journey as a character. While many assumed that he would be responsible for leading a Stormtrooper uprising (something that would have occurred in Colin Trevorrow's Episode 9), he instead comes full-circle by totally destroying the militant organization that stole his childhood and identity from him. By making Finn the one to finally destroy the last the First Order and the Empire, he earns his place as one of the most important heroes in the Star Wars mythos.