Hall of Termination
Once in the Hall of Termination, head up the stairs and then up the stairs above those. Attack the wall to get an MP Max Up. From here, jump onto the chandeliers and use those to traverse across. Go through the exit in the bottom left corner. Continue forward into the next room and traverse across the floor. Continue up to the upper left corner. In this next room, go through the middle left exit to find a stained glass portal room.
In the exit beneath this stained glass portal room, there is a bookcase you can inspect for some backstory. Head left to find a Save Room.
Exit this Save Room and go through the middle exit on the right. In here, climb the stairs and proceed through the door on the right. In this room is a boss door.
Boss Fight: Gabel
For a seemingly final boss fight in a game, Gabel is laughably easy. He mostly uses lightning, ice and fire attacks but because he telegraphs these moves so much, and because of how slow they’re casted, you can simply jump to a safe spot behind him long before the magical projectile is released.
Basically, just keep Welcome Company going and slash at him constantly with Zangetsuto.
When Gabel goes down, the rest of the game will play out and you’ll learn you got the bad ending, or rather, not the true ending because a game over screen appears. However, you will unlock the boss rush mode following this fight so if you feel like doing that, head to the main menu.
If you saved before Gabel and wish to get the true ending instead, continue forward in the guide.