Rokudai is the son of Taira no Koremori, and the last of the Heike line to perish. During his appearances in Chapter 12, the audience develops sympathy for him because he is targeted to be killed at such a young age. His nurse is able to find a way out of the execution by having a monk, Mongaku, take him as his disciple. This event ties into the common idea in Chapter 12 of the role of monks, and how they have more influence than a common citizen of that time.
As Rokudai ages, Yoritomo starts to see himself in the boy. He recalls that the reason he was able to come to power was because his life was spared during his father's - Minamoto no Yoshitomo - rebellion; if he spared Rokudai’s life, he feared that Rokudai would overthrow him and seize power. With the addition of Mongaku on Rokudai’s side, Rokudai posed an even greater threat to Yoritomo since he lost an ally.
Afraid that history would repeat itself, Yoritomo tried to secure his position in the capital by executing Rokudai. Unfortunately for Yoritomo, Rokudai was able to escape execution by becoming a monk. Yoritomo finally passes away, and Rokudai is thought to no longer be at risk for execution. However, Rokudais ultimate fate comes back to him once Mongaku revolts. The Genji capture those involved, and while Mongaku is merely exiled, Rokudai is sentenced to death. Rokudai’s death officially ends the line of the Heike, thus ending the novel as well.
What was the purpose of including the storyline of Rokudai in the official last chapter of the tale? Could he been seen as a literary device to end the novel in a clean, full-circle way? Should the audience pity him? These are questions to consider when looking at Rokudai’s character.