The Star Guardian skins are inspired by 'magical girl' anime such as Sailor Moon and they play a special theme song during recall and are usually distinctively bright in the game.
In the lore for this skin series, a group of high school students become 'cosmic protectors', led by team captain Ahri and her second in command Miss Fortune. There are also Pajama Guardian variants for half of the Star Guardians: Ezreal, Lulu, Lux, Miss Fortune and Soraka.
Every Star Guardian skin features a familiar, with owl pair Riku and Saki for Rakan and Xayah, Zoe's familiar is called Ran while Neeko has a frog called Towa.
This set of Star Guardians have appeared notably darker than previous versions and while it has been clarified to be a side effect of using abilities, there are lore reasons for their appearance.
In the splash art for Zoe, the 'corrupted' nature of her Star Guardian skin is on display with a sinister-looking Ran by her side, while Neeko looks far more like the traditional bright Star Guardians from previous years, the only Star Guardian without prominent darkness in their art.
Each of the Star Guardian skins will have prestige editions available to unlock throughout the corresponding event, giving the skins some golden flair. The event and skins could reach the main LoL servers as early as tomorrow with the 9.15 patch, but it is more likely they spend some more time in the PBE before release.