How to Obtain
Players can get a character's Stella Fortuna by obtaining a duplicate of the character from Wishes, or by obtaining the character through other means, such as buying the character from the Paimon's Bargains shop or through certain Events, both of which require having acquired at least one copy of that character prior as well to get the Stella Fortuna.
Since a character has 6 constellations, Stella Fortuna can only be acquired a total of 6 times per character, which implies getting the character 7 times in total. Getting further duplicates of a character through Wishes will instead increase the Masterless Starglitter from 2 to 10 and 5 to 25 for 4 star and 5 star characters respectively.
Each character has their own version of Stella Fortuna, and despite sharing the same icon, Stella Fortunas of the same rarity cannot be used interchangeably (Example: Diluc's Stella Fortuna cannot be used to unlock a Klee constellation and vice-versa) nor is there a version of Stella Fortuna that can be used on any character.