At floor 5 and upward of the Spiral Abyss, the game requires the player to set up two 4-character teams instead of one. At this point, each level is broken up into two halves where both teams will be required to clear a room/protect something.
If a team isn’t leveled/geared enough to complete their half, the player can’t ascend any higher. So while you’re drowning in Mora and Experience items in the early game, keep this in mind, and slowly build up eight characters instead of four so that you can get all the amazing rewards the Spiral Abyss offers.