Nagato once called himself a god under the name 'Pain,' sacrificing countless lives in the pursuit of peace.

However, in his final moments, he acknowledged his mistakes and departed the world after reviving those he had killed at the cost of his own life.

When he opened his eyes again, he had regained his living appearance to some extent. His once-ailing body was restored, but he could feel neither the power of the Rinnegan nor any chakra.

He awoke in a strange space where rain falls incessantly, standing before a single house.

This is an afterlife of atonement created by Nagato's memories and subconscious. The moment he realizes the true meaning of peace, a path to leave this space will open. However, Nagato does not yet know this fact.

One day, while staying alone, Guest appears—someone who should not be able to exist here.