There is no denying that players of the Elden Ring never stop discovering new things. Recently discovered legend provides some new information about Radahn, Ranni, and the sorceress Sellen. People, buckle up because we really doubt you'd ever consider playing events through in this sequence.
After starting Ranni's questline but before the festival begins, you may acquire some intriguing lore by speaking to Sir Jerren, the person in charge of organizing the Radahn Festival at Redmane Castle. Speak to Jerren rather than Selvius or Sellen when Blaidd instructs you to do so regarding Nokron.
On the way to Carian Manor, there is a huge blacksmith named Iji. You can inquire about him. He informs you that Iji produced blunt, but effective against the Scarlet Rot, weapons for Radahn's soldiers. This suggests that before the Shattering, the Carians and Radahn were allies.
Jerren also informs you that the festival will determine Ranni's fate, demonstrating his awareness of the impact the stars' stabilization is having on the Carians. Iji would then reproach himself for not seeing sooner that conquering Radahn will free the stars, restarting the Carian's fate and maybe exposing the city of Nokron if you go see him.
It's wonderful to know that FromSoftware had really planned ahead and set breadcrumbs throughout the game because it did all feel a little weird when these things simply seemed to unexpectedly start off after the festival. Iji and Jerren are quite literally on opposite corners of the game's vast planet, making it difficult to travel between them. It is unclear how on Earth we were supposed to discover them.
This does, however, emphasize that Caelid is a location that is meant to be explored later in the game, not immediately following Limgrave. After explaining Iji's hypothesis to Blaidd in the underground city, the two of you can go for the festival.
Finally, return to Iji after murdering Radahn, and he will explain that the star-stopping that gave sorceress Sellen her immortality was the reason for it. Radahn was actually essential to several plotlines. What a huge burden he was carrying. Hence, that's why he started practicing gravity magic.