Yashio, also called Zushio or Zushiomaru, hails from a respected family where his father served as an officer protecting a forest. False accusations of arson led to his father's trial in Kyoto. Forced to abandon their home and surrender their land to a new owner, the family attempted flight. They were ambushed by bandits who deceived and scattered them. Yashio and his sister Anju were captured and sold into slavery.

This plunged Yashio into brutal conditions, enduring harsh labor under a cruel master. Throughout enslavement, his resilience centered on protecting Anju and reuniting with their parents. The siblings clung to each other for survival and emotional support, constantly yearning for their lost family. Their mutual protection defined their existence.

Yashio's background as displaced aristocracy starkly contrasted with his enslaved reality. The trauma of separation and forced labor shaped him, forging endurance and unwavering familial loyalty. His relationship with Anju remained the core of his character as they navigated exploitation and adversity together.