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.
Here are some useful posts and links that might help: 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 ! Some users reported that Patch 1
Or, visit the Steam Community page for SFxT: https://steamcommunity.com/app/1210 which includes various bug fixes
** GameFAQs and Steam Community:** You can also check the GameFAQs page for Street Fighter X Tekken on PC: https://gamefaqs.gamespot.com/pc/2420-street-fighter-x-tekken/
You can download the patch from the official Capcom website: http://www.capcom.com/support/sfxtpc_patch.html
Some Reddit users shared a link to a thread with a : https://www.reddit.com/r/StreetFighterXTekken/comments/1jyy13/character_unlock_tool/