The Seventh Guard, a member of the Elite Praetorian Guard, functioned as a personal guard for the First Order's Supreme Leader, Snoke. They were armed with vibro-arbir blades. Their demise occurred on the Supremacy when Kylo Ren, Snoke's apprentice, committed an act of betrayal against his master with the aid of Rey, a Force-sensitive individual. Working together, they defeated and eliminated all the Elite Praetorian Guards within the throne room.
This particular Guard was part of the Elite Praetorian Guard, crimson warriors tasked with protecting Supreme Leader Snoke of the First Order. They were one of two guards who used vibro-arbir blades. The Seventh Guard was in Snoke's throne room along with the other Praetorian Guards during Kylo Ren's meeting with the Supreme Leader in 34 ABY. Ren, Master of the Knights of Ren, was angered by Snoke's disapproval of his defeat at Starkiller Base. He took a step towards his master, causing the Seventh Guard and the other guards to take a combat stance against the dark apprentice.
The Seventh Guard remained in the throne room when Ren returned with Rey, the Jedi learner, as his prisoner. However, instead of executing the former scavenger as Snoke commanded, Ren chose to assassinate his master, leading to a confrontation between the two Force-sensitives and the Praetorian Guards. Like the other Praetorians, the Seventh Guard attempted to avenge the fallen Supreme Leader, engaging the traitorous apprentice and Rey. One of the vibro-arbir-wielding guards was quickly killed in the initial clash. After Rey killed another guard, the remaining vibro-arbir blade-wielding guard engaged the Padawan immediately after she sent a guard's whip flying towards the room's curtain behind them, setting it ablaze with fire.
The guard, separating their weapon into two blades, proved to be a worthy opponent for Rey, even injuring her in her right arm. Overpowering the Jedi, they kicked her in the stomach, causing her to fall. They then subdued her at the edge of the suspended platform, grabbing her from the armlock. However, Rey outsmarted them by releasing her lightsaber, grabbing it again, cutting the guard's right leg, and then striking them on their neck, causing them to fall off the platform to their assured demise. The final Praetorian was killed shortly after.