Here's a workflow I created for making your own SC6 story screenshots with customized text, characters, and background. I initially created this for use during my streams as intermission screens, and since it's made to be used by only me I didn't exactly focus on making the process super duper user-friendly, but hopefully it isn't too fiddly to set up.
Full guide and download link can be found here: https://www.fluffyquack.com/news/soulcalibur-vi-storyline-screenshot-creation-guide/