King Elbas, Sepunia, and Noah didn't relax after they returned among the light. They immediately used their abilities to seal the cracks connecting that region to the void.
Sepunia and King Elbas ended up doing most of the work since Noah found himself unable to summon the entirety of his power while the parasite was still going wild. The plant severed its connection with the many seeds inside the void, but it resumed its expansion as soon as it sensed the light, and its violent hunger was strong enough to ignore Noah's suppression.
Noah had to stop focusing on the cracks to deal with the parasite. He spat flames and expanded the dark world balance what the plant was absorbing from his body, but his condition worsened since the environment couldn't provide energy fast enough.