Athos was right when he thought that spirits were capable of forcibly breaking through layers using accumulated energy, but it was information that not even the spirits themselves knew.
It was widely held information that spirits could accumulate energy over time and there was no known limit to the amount they could store, but only because no spirit had ever accumulated enough energy to do so.
Energy accumulate at an extremely slow rate and normal spirits could store dozens of times more energy than the mana core, so most normally form new layers before reach this limit.
Many used the accumulated energy to fight or create a suitable environment around it like a forest, so it was nearly impossible to accumulate enough energy to break through the force. Even if they encounter growth bottlenecks, it would take centuries to build up the necessary energy.
