The Gamble (賭け, Kake) is the 11th episode of Muhyo & Roji's Bureau of Supernatural Investigation anime series.
Rio continues her relentless attack on Muhyo and the others, refusing to even listen to the fervent pleas of her own pupil, Bico. Those who have sold their souls to a messenger of Hell using forbidden magical law can never be human again... but Muhyo says there may be something they can do for Rio. However, he needs to recover from his mental numbness in order to do it. Backed into a corner, the team gambles everything on a secret formula concocted by Bico to help him temporarily recover...
Rio summons a large fire salamander and goes after the group. Biko tries to talk to her, but Rio ignores her and makes the salamander shoot a fire attack. Yoichi uses a barrier and protect all of them. He explains that those who sold their souls to messengers of Hell can never be human again. But according to a precedent, their only choice is to judge her in her half-spirit form, while her sins are still minor, which would mean she needs to go to Purgatory. Muhyo asks Biko to create a potion that will temporary restore his ren. Biko comments that the most secret of the secret formulas, but doesn't want to make it knowing it will be used to kill her teacher. Muhyo tells her he didn't say he will kill her, but may end up needing to send her to hell if she becomes an evil spirit.
Yoichi prepares a more powerful barrier, blocking multiple attacks from the salamander, while Biko works on the potion and recalling how Rio was teaching her the formula. Enchu warns Rio that Muhyo is planning something and she becomes more aggressive with her attacks. Biko finally finishes the Ren Source Spring potion. Biko explains what Rio had told her about it, that it originates from 700 years ago when there was a great battle between spirits and executors. As the spirits greatly outnumbered the executors, the potion helped them, but taking too much of it will poison the body and the executor will die.
Muhyo decides to drink the whole glass and tells Yoichi to remove the barrier after the next salamanders attack. Rio realizes Muhyo had overcome his mental numbness and he uses a Anesthetic Needles to make Rio drop her staff, and fell asleep. Yoichi then destroys her staff, causing the salamander to disappear. Muhyo wants Yoichi to place a messenger gate, and he wonders what Muhyo plan is. Muhyo explains that they need to defeat the messenger she made contract with and that will render her contract blank. As they prepare the gate, Yoichi notices a travel magic circle and then they see Enchu standing next to Rio.
Meanwhile, Reiko escapes the prison with Maeda, who tells her he saw someone opening the prison doors. Yoichi confronts Enchu and realizes that the executors that ignored Rio when she needed help for her mother, has been killed. Muhyo taps his book twice and Yoichi recognizes the signal to create a blind stop and gets close to Biko and then pushes him away, allowing Muhyo to cast Anesthetic Needles, but that had no effect on Enchu. Enchu explains that Anesthetic Needles are one of the most common ways to fight humans, but he is becoming less of a human with each passing day. He explains that his plan may work to save Rio, but its too late to save him. Enchu then uses a spell and removes all the talismans in the prison. Teeki then unites all the spirits into one and they go to Enchu.