JJ Abrams says he and Star Wars creator George Lucas talked about midichlorians during their discussion for Star Wars: The Rise of Skywalker. Lucas introduced the concept of midichlorians - microscopic organisms that allow beings in the Star Wars universe to use the Force - in 1999's Star Wars: Episode I - The Phantom Menace. As the Jedi Master Qui-Got Jinn explained to a young Anakin Skywalker in the film, midichlorians "continually speak to us, telling us the will of the Force".
This year's The Rise of Skywalker will serve as a conclusion to the Skywalker Saga that began in the real-world with 1977's Episode IV - A New Hope, but started chronologically with the introduction of young Anakin and his mother Shmi during The Phantom Menace. The ongoing Star Wars sequel trilogy has already directly acknowledged important events from Lucas' prequels, with an older Luke Skywalker mentioning the rise of Darth Sidious and the fall of the original Jedi Order to Rey in Episode VIII - The Last Jedi. However, the all-too controversial subject of midichlorians has yet to be explicitly discussed in the recent films.
Speaking to Total Film (via Games Radar), Abrams revealed he had a meeting with Lucas before starting production on The Rise of Skywalker. The filmmaker confirmed they talked about the idea behind the Force and the themes Lucas was focusing on when he wrote A New Hope more than forty years ago. As a result, the topic of midichlorians eventually came up.
“Yes, there were some conversations about Midi-chlorians - he loves his Midi-chlorians. But it was a very helpful thing. Sitting with him is a treat, just to hear him talk, because it’s fucking George Lucas talking about Star Wars. I always feel it’s a gift to hear him talk about that stuff. Because the effect that he had on me at 10 years old is utterly profound.”
Lucas actually came up with the idea of midichlorians while working on A New Hope in the late '70s, but ultimately decided to leave them out of the original Star Wars trilogy, only to revisit them in the prequels about two decades later. Fans (and even writers who've worked on Star Wars novels and comic books over the years) have long expressed mixed feelings over the concept, with some appreciating the scientific explanation behind Force powers and others arguing it diminishes the Force's spiritual side. It's worth mentioning, however, that Abrams didn't say anything in his comment about The Rise of Skywalker explicitly referencing midichlorians; rather, it was simply a concept that came up while he and Lucas were discussing the Skywalker Saga's greater themes and ideas.
Keeping that in mind, it's certainly possible midichlorians will factor into The Rise of Skywalker. For example, they could be connected to how Emperor Palpatine returns from the dead in the film, or somehow come up during a discussion about Rey's own link to the Force. It's not, per se, necessary for The Rise of Skywalker to name-drop midichlorians at some point, but it's an idea that should (and probably will) be acknowledged one way or another. After all, love 'em or hate 'em, they're a core element of the Skywalker Saga and the larger Star Wars mythology.
Source: Games Radar