Ieyasu was a childhood friend of Tatsumi and Sayo that set out on a journey to the capital to earn money for their village. He seemed to have a bad sense of direction and was a known troublemaker.

During their journey, they were attacked by night bandits which separated them. He managed to stay with Sayo and got invited by Aria to her mansion. They were served with a meal that made them lose consciousness. He was put on drugs which made him suffer from the "Lubora disease." He survived until Tatsumi and Night Raid arrived at the place where he, Sayo, and other people that were lured by Aria and her family, were imprisoned. He seems to be glad when Tatsumi killed Aria. He then succumbed to the last stages of "Lubora disease."

Ieyasu was shown to wield an axe. He presumably possessed combat abilities on par with Tatsumi, as they and Sayo trained together since they were little.