The Reactor Core mission pack consists of 4 Special Missions, and is unlocked after you've completed the Omegachi (which will grant you've already unlocked Aurae Saga. You can do 4 missions in a row as a continuity, or you can do one mission, exit and complete the next ones later, like checkpoints. Your towers and rounds progress will be saved after each mission, and all of them will be transferred directly to the next mission whether you play it continuously or you exit and play later. You'll get 70,000$ starting cash in this mission pack. Here're the missions of the pack: