Background
Yosmo Oishi was born in 1659. His common name was Kinai, which he later changed to Kuranosukc. His great-grandfather Oishi Yoshi- katsu, who was in the service of Asano Nagashige, was made hard (chief retainer) as a result of his achievements in the siege of Osaka Castle and assigned a stipend of 1,500 koku of rice. His father died young.
Career
After his father's death it was Yoshio who succeeded his grandfather as chief retainer of the Ako domain. In 1701, just twenty-five years after he assumed that post, the lord of the domain of Ako, Asano Naganori, was ordered to take charge of the reception of an imperial envoy at the castle of the shogun in Edo. The shogunatc official Kira Yoshinaka failed to give him proper instruction in the rules of ceremony to be observed, and as a result he was publicly humiliated. In anger he drew his sword and wounded Kira, though such conduct was strictly forbidden within the confines of Edo Castle. Asano was punished by being deprived of his domain and ordered to commit suicide.