Stella fortune are Constellation Activation material items used to activate the constellation of playable characters, except the Traveler.
Players can obtain a character's Stella Fortuna by obtaining a duplicate of the character in the wishes, or by obtaining the character through other means, such as buying the character in Paimon's Bargains store or through Events, which require to have acquired at least a copy of that character before obtaining the Stella Fortuna.
Since a character has 6 constellations, the Stella Fortuna can only be acquired a total of 6 times per character, which means obtaining the same character 7 times. Getting more duplicates of a character through Wishes will increase the Unowned Starburst gained from 2 to 5 for 4-star characters and from 10 to 25 for 5-star characters.
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 (for example, Diluc's Stella Fortuna cannot be used to unlock a constellation of Klee and vice versa) nor is there a version of Stella Fortuna that can be used on any character.
The equivalent of the Stella Fortuna of the Traveler is the Memory of the Four Winds, Memory of immovable crystals and Memory of the violet flash for its constellations Anemo, Geo and Electro respectively.