A Sonic and the Black Knight version of Stellar—Lady Archfedd, daughter of King Arthur!
Some lore:
Came to be when King Arthur and Sir Lancelot unknowingly laid together upon a fairy mound, resulting in the fey gifting (or perhaps cursing) the King with a changeling child. Despite Lancelot's protests, Arthur accepted the infant as his heir.
Lancelot is half fey himself in this AU, and thus has a wide knowledge of fey culture and behavior (the fairies in this AU look a lot like Black Arms aliens from canon).
Despite his initial reservations, Lancelot does eventually grow to see Archfedd as his daughter.
Due to Arthur and Lancelot's relationship being secret, in public Archfedd is simply known as the King's daughter.
Archfedd learns of her fey heritage in her teens.
A skilled swordswoman, her fighting style is like that of a dancer, slashing out with twin blades.
Her swords are dubbed Efeilliaid Eira—the Snow Twins. Said to almost shine blue in the midst of combat.
Being of fey heritage, her armor had to be specially crafted as to not harm her. Pure, precious metals such as gold, silver, and cold iron all burn her skin.
Despite being trained in combat by each of the knights of the round table, it is rare she actually gets to fight alongside them.
Alt fey form appearance: