Star Wars Jedi: Survivor’s teaser trailer shows off a brief duel between Cal Kestis and a mysterious Dark Side character, but he only ignites one half of the lightsaber, which raises questions over what kind of blade he'll wield in the game. Cal's lightsaber is unique, and the story of its creation is integral to Cal's character development. So few characters in Star Wars wield double-bladed lightsabers that it’s hard to imagine why Respawn has seemingly moved away from the double-bladed style featured in Jedi: Fallen Order. However, there is a possible explanation for Cal’s absent double-blade, and it could relate to Nightsister Merrin.
[Warning: This article contains spoilers for Star Wars Jedi: Fallen Order.]
Cal’s former Jedi Master, Jaro Tapal, wielded a double-bladed lightsaber during the Clone Wars, but it was damaged during Order 66, leaving only one side intact. He gave it to Cal before he died during the events of Order 66. Later, when Cal visits Dathomir, the lightsaber is destroyed during a Force vision. This prompts Cal to travel to Ilum to build a new one. Cere Junda, Cal’s new master, offers her old saber to help with the process. Ultimately, Cal combines the sabers of both his masters to form a double-bladed lightsaber. This added new moves and abilities for the player to use in combat, making it one of the coolest features of Star Wars Jedi: Fallen Order. His new saber could also be split, providing the ability to wield one side in each hand, similar to Asajj Ventress' weapons in The Clone Wars animated series. This is an interesting detail that shows how Cal differs from other surviving Jedi. It also hints at what’s to come in Jedi: Survivor, which will be explored later in the article.
Removing Cal’s double-blade entirely from Star Wars Jedi: Survivor seems pretty unlikely, as it would be an asset to the game’s combat. With that in mind, it's possible that it was hidden for narrative purposes. One popular theory that has been discussed by YouTube channel Star Wars Explained explains that the other side of Cal’s lightsaber isn’t missing, but instead that he removed it and gifted it to Nightsister Merrin for Jedi training. She is already Force-sensitive, as the Nightsisters of Dathomir use magic that draws from the dark side. So it would make sense that Cal and Cere could be training her, especially given rumors about Jedi: Survivor’s new playable character.
Star Wars Jedi: Survivor - Cal Could've Given Merrin Half Of His Lightsaber
Star Wars Jedi: Fallen Order foreshadows Merrin’s potential to be a Jedi just before the Taron Malicos boss fight, so it would make sense for this thread to be developed further in the sequel. Cal and Merrin talk about what qualities make a true Jedi and the purpose they serve in the galaxy. He gives her his saber to prove he isn’t a threat to her. She ignites it and tells Cal about how General Grievous slaughtered the other Nightsisters during the Battle of Dathomir. The game highlights the similarities between the Jedi Purge and the Massacre of the Nightsisters and the qualities Cal and Merrin share as a result: they are both survivors. Cal’s story helps set Merrin on a new path, and she joins his crew because of it. This opens the possibility for Merrin to become a Nightsister Jedi in Star Wars Jedi: Survivor.
Another circumstantial hint that supports this theory is the split lightsaber. The split-saber is an even rarer type of lightsaber than the double-blade. One notable character who also wields a saber like this is Asajj Ventress. She was also a Nightsister and a strong force wielder trained by Count Dooku. Ventress’s potential to be trained in the Jedi ways may further hint at Merrin wielding the other half of Cal’s lightsaber in Star Wars Jedi: Survivor, which may explain why it was absent from its reveal trailer.
Source: Star Wars Explained