You're looking for a PC patch to unlock all 108 characters in Street Fighter X Tekken!
Keep in mind that some of these links or tools might not be up-to-date or supported by Capcom. Be cautious when downloading or using third-party patches. street fighter x tekken pc patch 108 character unlock link
Capcom released an official patch for Street Fighter X Tekken on PC, which includes various bug fixes, balance changes, and... character unlocks ! You're looking for a PC patch to unlock
Here are some useful posts and links that might help: which includes various bug fixes
Some users reported that Patch 1.02 (not 108 specifically, but close!) or later versions unlock all characters. You can try updating your game to the latest version.