They were in the tower that maintained a barrier that sealed away main antagonist, 'Beusbrichel'(extremely massive Eldritch entity, think of entity like Nyarlathothep) that had destroyed countless worlds. This game world is the last line of defense before 'Beusbrichel' broke free and will possibly consume Earth once freed. So they are trying their hardest to clear the tower because it is the source of energy that power-up the barrier.
Clearing more floors in the tower(100F) --> stronger barrier.

What is this even about anymore its been a minute can someone kindly give me a recap?