While keeping a close watch on the movements of the Shadow Mamonos, a sudden attack on the Mamono School takes place.
The mastermind behind it is Decay, a mysterious creature who seems to have memories of the old world and deeply resents the explorers.

Thanks to Richard's quick thinking, the explorers manage to repel Decay's attack, but its true objective remains unknown, and the danger is far from over.
With the emergence of new threats, the situation grows even more chaotic.

Amidst this, the explorers start to wonder about Paula, who is in the midst of her training, and decide to check on her.
Little did they know, this simple act would lead to an unexpected encounter...