Being raised alongside Shishou, Eishuku was like a brother to Shishou. When Shishou rose up against the corruption of Fu-ou's reign, Eishuku was his staunch supporter and eventually was given a position in Shishou's court. He steadfastly tries to support Shishou, even when it becomes apparent that the king's reign is beginning to tilt toward ruin while Shishou is too stubborn to find fault with his own vision of a prosperous kingdom.
When Daishou, the Taishi, is mysteriously killed and Junkou, the Taiho and the king's younger brother, goes missing, Eishuku and Shuka become involved in a supposed conspiracy against the king. After being placed under house arrest, they are ordered to escort Sairin to Sou and then return for their trial. Though the order is interpreted to mean that they should not return, Eishuku persuades Shuka to return to Sai out of duty to their country.
Soon afterward, Shuka realizes the true power of the Kasho Kada, the royal treasure of Sai that shows visions of prosperity, and recalls that Eishuku had suggested that Junkou present the Kasho Kada to Shishou in hopes of recovering the Way. After considering that the visions shown are subjective and ideal to the one using the treasure, Shuka confronts Eishuku for deliberately forcing Shishou's reign to tilt to ruin by ensuring that Shishou would not be able to see the flaws of his idealism. Eishuku attempts to deny responsibility for failing to see beyond idealism and for forcing Shishou's reign to end sooner, hoping to avoid being blamed for not being able to save him.
When Shishou unexpectedly abdicates his throne and takes his life, Shishou's last words have a devastating impact on Eishuku, who soon takes his life as well in order to accept responsibility for his actions.