Even though he used modern components when crafting his lightsaber, Kylo Ren went old school with its design. The extremely rare crossguard style dates back to the ancient Sith warriors who fought at the Great Scourge of Malachor 4,000 years in the past. This epic battle took place after Darth Tanis created a terrifying, gigantic kyber-based weapon, leading the Jedi Order to attack the Malachor Sith Temple that housed it.
However, Kylo Ren's decision to construct his plasma blade in the same fashion as these ancient warriors of the dark side was not just based on aesthetics — it had a practical purpose, as well. According to Pablo Hidalgo's "Star Wars: The Force Awakens – The Visual Dictionary," the kyber crystal that powered Kylo's lightsaber was cracked, which made the plasma stream unstable, so it had to vent out of the sides to create the crossguard blades, or quillons.
Kylo Ren cleverly added shielding over the base of the vents to make sure he did not cut his own hands off when wielding the weapon, but the legendary Sith warriors of the past would not have been impressed with his amateur construction. Hidalgo also says of the lightsaber, "It's crude appearance suggests construction by an inexperienced hand."
