Rengoku 2: The Stairway To H.E.A.V.E.N. H.E.A.V.E.N. mode
Defeat Gryphus (Stage 8 Boss), then go through the door behind you when you re-enter Primordium (Level 0), after the sequence, to unlock Heaven-A, -B, and -C.
Highest floor in H.E.A.V.E.N. mode
Successfully complete all 99 levels in H.E.A.V.E.N. mode to unlock the highest floor.