itch.io

Got it. What tripped me up was that the three labyrinths had different amounts of orbs. That said, there's something I feel I should inform you of; after I got the three labyrinths completed and rescued Oriel, when I returned to the library and freed the elemental beasts, then entered the underground door (no need for any new keycards, the door just opened.) 

After entering, the scene with Kamran and Mercury repeated itself. After the scene ended, I beat the high priest and entered the knife chamber (didn't grab the knife, just took the two treasure chests and left), after I tried to leave, the cutscene where Melody shouts at Kamran to tell him the fort is under attack also repeats, and from there I went to the fort, and Dominus was back in the cell. 

After talking to him, I was automatically sent to Red Wall Village, and Mercury left my party (probably because he leaves when the scene is originally shown.) Anyway, I reloaded my save from the knife chamber, and after the Melody scene forcibly removed me from the library I just proceeded to the next area, where the game continued on as normal.