Star Wars: The Acolyte gave us a glimpse of an important Sith ritual, sort of

polygon.com:

Lightsabers are the bread and butter of Star Wars. Even when the rest of the story is a mess, you can usually count on the series to employ its signature glowing swords to pretty rousing effect. And like everything else in Star Wars, the story behind lightsabers is full of lore and details. Among the most important of those details is the lightsaber color, and the season finale of The Acolyte gave us one of our best looks ever at how the Sith sabers take on their terrifying crimson hue.

Lightsabers are powered by kyber crystals, which are small Force-sensitive rocks. Once a Jedi builds their saber, the crystal picks up their unique Force energy and transforms into one of a variety of colors — mostly the ones we’re familiar with from the shows and movies.

When a Sith gets a lightsaber, generally one they’ve taken from a Jedi, they pour all of their rage and hatred into the crystal, overwhelming the light side energy of the previous owner. This causes the crystal to transform into the familiar red through a process called bleeding.

This is, it seems, what we watched happen with Osha in The Acolyte. Sure, it’s a little bit of a strange way to react to being told that her mother was killed by Sol on accident. But it appears that after she murdered him and picked up his saber, she channeled her feelings into his kyber crystal without even trying.

On top of that, we also got a much weirder and more biologically literal caveat: She seems to have literally bled into the kyber. It’s not really clear that this changed anything, or was an important part of the process, but it’s certainly a more a visual way to make the otherwise arcane and opaque process a little more literal. And, who knows? Considering what else The Acolyte has been about — maybe this is how the process of bleeding kyber crystals got its name.