Rift seeds were how a rift could dominate territories. Monsters from the main rift would carry the seed and plant it into a ruin, thereby creating a mini version where monsters would continue to sprawl, and the ruins around it would be greatly strengthened.
The monsters from this core—an area where the rift seed ruin and strong ruins are concentrated—would also try to plant more rift seeds into other ruins. The reason being, the rift seed ruins were where monsters could freely come out and attack people.
Atrox got the main gist then. The Ten stayed in the core as the strongest team and tried to destroy this rift seed ruin, but they hadn't yet... because the Ten were from different Flags, and each was subtly trying to keep the others in check to prevent them from reaping the reward from this ruin.
But mainly because even without the seed, the core was a place where strong ruins continued to sprawl every time.
