The save file is named sfxt_save.dat . You'll need to modify this file to unlock all characters.
To unlock all characters, you'll need to edit the sfxt_save.dat file. You can use a hex editor like HxD or a save editor like Savegame Editor to modify the file. Street Fighter X Tekken All Characters Unlocked Pc Save File
C:\Users\<YourUsername>\AppData\Roaming\Capcom\SFxT\Savedata The save file is named sfxt_save