I didn't know...

I'm currently tackling Tartarus in Chapter 6 of the main story. I reached the 'Thunder Spear' and was progressing smoothly, albeit struggling with the battles. After defeating Titan at the 'Thunder Spear', you can't proceed to the next story until the spear is fully charged. At that point, I made a huge misunderstanding and thought, 'Maybe the next story will unlock once all three groups reach the 6th floor?', so I proceeded without starting the charge. I only realized a few minutes ago that I actually needed to start the charge….