Throughout Chapter 12 in the Tale of the Heike, the role of monks is prevalent. They function as a sort of deus ex machina, randomly inserting themselves into the plot to either resolve or start conflict. This plot device is seen multiple times throughout the chapter, by both Mongaku and Tosabo. Along with this, they consistently take advantage of the title that ‘monk’ gives them, using their influence in a way that could be morally questionable.
When Rokudai was supposed to be executed for being in the “Heike clan,” it was only Mongaku wanting him as his disciple that set him free. His family's begs and pleads meant nothing to Yoritomo because they were commoners. Mongaku exercises his power by continuously giving Yoritomo a head that he claims is Yoritomo's fathers. In the first instance, Mongaku used the head to evoke a rebellion by Yoritomo that would benefit himself in the process. In the second instance, it seems more so as a way for the novel to recognize Yoritomo's father and the accomplishments he achieved while alive.
Tosabo also demonstrates the power of his title in the chapter. When Yoritomo sends him to assassinate Yoshitsune, Yoshitsune is immediately aware, and threatens to kill Tosabo. In order to avoid failing his mission, Tosabo does something that would only have meaning as a monk - he writes oaths that he burns, swallows, and offers at shrines. Yoshitsune believes these offerings for they are usually not to be taken lightly, so he gives Tosabo his trust. He realizes this was a mistake when Tosabo attempts to murder him that very night. This event begs the reader to ask: had Tosabo not been a monk, would his oaths have been accepted? Would a common person have been killed on the spot instead of getting a chance to explain themselves? Are the monks to be trusted?
Musashibo Benkei Brings the Captured Tosabo Shoshun to Yoshitsune from the Collections of the Art Institute of Chicago: