Episode 31

A Wolf in Sheep's Clothing is the sixth episode of Ao no Exorcist's second season anime.

Synopsis
Todo and Mamushi escape to the old Myoda stronghold. Todo leads Mamushi to believe the eyes will be the safest held there. Inside Mamushi discovers the sacred flame is still being tended to there.

Tatsumi's letter informs the Koma sword is also the Kurikara and its history. When Shiro was trying to take the sword, he was severely wounded and collapsed while Yaozo tried to retrieve it from him. When Shiro woke up in the temple, Tatsumi asked him why he wants the sword. Shiro says it was to kill a child and Tatsumi demanded he left. Shiro told Tatsuma he refuses to leave without it and storms through the temple, discovering the room of people affected by the miasma. He treats them, saving their lives and in return asks for the sword.

Tatsuma's father tries to have Shiro seized, telling Tatsuma he will be punished for allowing an Exorcist into their temple. Tatsuma tells his father he isn't protecting Myoda, only the rules. Tatsuma gives Shiro the sword and helps him escape. Shiro was surprised by this change of heart, but Tatsuma explains he knows the sword is empty because he drew it as a child. He also believes Shiro wouldn't kill a child. Before leaving, Shiro tells Tatsuma they are more than even and are now friends. Months later the Blue Night occurred and Tatsuma learns the Myoda secrets as his father dies in his arms.

Todo and Mamushi enter where the secret of the Myoda is held, revealing that the Impure King is subdued below the original stronghold. Todo reveals his true form to Mamushi, before he can kill her, Tatsuma intervenes with a gust of fire. He promises to return Mamushi to her father and that the Impure King will end with him.

When Tatsuma's father died, Karura revealed themself to Tatsuma. Karura informs Tatsuma they feed on lies, secrets and distrust in exchange of their services. Tatsuma uses Karura to battle Todo. Todo returns the Eyes to The Impure King. Juzo arrives as the King awakens, Tatsuma has him take Mamushi back to her father and asks her to tell everyone the truth. Todo mortally wounds Tatsuma after Tatsuma used his personal pact with Karura to hold the Impure King at bay. Todo reveals everything he has done was to get Karura. Todo forced Karura to possess his body, forcing his will onto them.

The end of Tatsuma's letter asks Rin to use his sword to defeat the Impure King.