These are the requirements in order to unlock specific content on Guardian Tales:

Unlock RiftClear World 1 (Tutorial)
Unlock TowerClear World 1 (Tutorial)
Unlock HeavenholdClear World 1 (Tutorial)
Unlock Guardian Base CampClear World 2
Unlock Side StoryClear World 3
Unlock Tower of HorizonClear World 4, Stage 6
Unlock MultiplayerClear World 4
Unlock Orbital LiftClear World 6
Unlock Training RoomClear World 7, Stage 5
Unlock Heavenhold Tower Clear World 7, Stage 5
Unlock Mirror RiftClear World 7
Unlock Kama-ZONEClear World 9
Unlock Exploration ForgeReach Guardian Level 100
Unlock Sealed GoddessUnlock Plitvice with 1,000,000 Soul Points
Unlock Mysterious MachineUnlock Libera with 3,200,000 Soul Points
Unlock Expedition (Exploration Forge)Clear World 13 quest - The Chosen One
Unlock Farm (Exploration Forge)Clear World 7