Lazarus: "I wasn't Bluffing"
The trapped Rankers soon realized their attacks on the Runic Birdcage Barrier were only empowering the domain.
After several futile attempts, the Birdcage Barrier began reflecting their attacks back at them, inflicting injuries or even death upon them.
No Ranker was foolish enough to launch an attack on the Runic Birdcage anymore.
Eren's comrades, the ones holding the Gluttony Pearls, acted as the Runic Eyes for the massive Birdcage Barrier. They were isolated from the trapped Rankers, ensuring they could maintain the barrier without worrying about attacks from within that could disrupt the Runic Formation.
***
Beelzebub had provided Eren with this barrier-type formation simply named Birdcage Barrier. It required only five S-Ranked Gluttony Pearls as the minimum power source to activate. However, it could benefit from additional Gluttony Pearls, strengthening the formation beyond the bare minimum requirement and making it more dependable.