No. 6
The Reason for That is... (1x8)
:
In order to save Safu, Shion and Rat head to the edges of the Western District. There, they meet a legless old man who leads a large group of men. The old man, the person who named Rat, is actually one of the researchers with the young Karan in Rikiga's picture. The man tells Shion that he was the real first survivor of the parasite bees. He also states that Rat is the last survivor of the forest folk who were wiped out by No. 6. After Nezumi has another vision with the winds and the singing like he had before while he was singing, he repeats the song to the legless man and the water around them begins to glow. The legless man tells them about Elyurias, the reason No. 6 destroyed the forest folk.