Kylo Ren's (Adam Driver) lightsaber crossguard design was apparently inspired by the Luke Skywalker's (Mark Hamill) from the original Star Wars poster. Debuting in 2015's Star Wars: The Force Awakens directed by J.J. Abrams, the character was poised to become the primary villain of the sequel trilogy. He ruthlessly killed his father, Han Solo (Harrison Ford) when he attempted to bring him home and he even crossed his own master when he betrayed Supreme Leader Snoke (Andy Serkis) in Star Wars: The Last Jedi.
As the grandson of Darth Vader, Kylo Ren worshipped his grandfather. Much of his aesthetic was patterned from the legendary Sith's outfit, complete with the mask and flowing cape. There were some tweaks, but overall, it's clear that the former Ben Solo was trying to emulate Vader to a degree. One particular character design for Kylo Ren that separated him from Vader was his red lightsaber which had beaming crossguards on its hilt. This, as it turns out, was based on Luke's lightsaber design from the classic poster for the original Star Wars movie.
Lucasfilm creative art manager Phil Szostak shared the info on his Twitter account, revealing that they based Kylo Ren's lightsaber from Luke's as seen in the one-sheet for the 1977 Star Wars flick. In the poster, created by Tom Jung, Luke holds up his weapon with lateral beams emanating from it. Check out the images he shared for reference below:
In-universe, Kylo Ren's lightsaber was made from his original one while training to become a Jedi with Luke. Originally, it had a blue blade, however, after his falling out with his uncle and eventual fall to the dark side, becoming the subordinate of Snoke and leader of the Knights of Ren, he re-constructed it to have a red blade. He based its cross guard hilt from an ancient design going back to the Great Scourge of Malachor. Containing a cracked Kyber, it required lateral vents on either side of the handle to redirect extra heat from the crystal. Kylo Ren used the said saber for the most part of his sequel trilogy journey. However, he eventually got rid of it in Star Wars: The Rise of Skywalker when he decided to reclaim his Ben Solo persona. Throwing his corrupted lightsaber away, he used Anakin/Luke's blue lightsaber in tandem with Rey (Daisy Ridley) as they fought Emperor Palpatine (Ian McDiarmid) together.
Prior to the release of The Rise of Skywalker, Lucasfilm released a poster for the Skywalker Saga capper that recreates the classic Star Wars one-sheet. It successfully evoked nostalgia for long-time fans of the franchise. However, since Kylo Ren's eventual return to the light side is similar to how Vader's at the end of Return of the Jedi, they weren't really able to parallel the imagery of Luke holding the lightsaber that was the design inspiration with him.
Source: Phil Szostak