Soma Cruz has a secret Easter egg challenge. .
If you escape a trial as Soma with all three of the Soul charms (Flame Demon, Succubus and Giant Bat) from the rift equipped on him, you'll unlock a second portrait badge for him named "Soma's Dark Side."
Comments
This is how you got the true ending in Aria of Sorrow. By equipping those three souls when fighting Graham.
But I did not equip a single charm after they reworked the UI. Especially the Charm Menu is straight out of hell.
Does this secret challenge have to be completed before the Tome closes?
That's likely not something that can be answered except by a developer.