Masayoshi was previously part of the elite group known as the Gotei 13 and traveled alongside the Partisan Squad on a mission to hunt down rogue spirits called Hollows. During this time, he shared a close bond with Yachiru Kusajishi, who brought sweets to their meetings and they enjoyed them together. Masayoshi was also married at the time, but an argument with his wife just before leaving for a mission led to her tragic death. Unbeknownst to him, he had been possessed by a Hollow during this mission, which caused him to kill his own wife as the Hollow. The trauma of this event made Masayoshi forget what happened and he blamed an unknown Hollow. This incident deeply affected him and led him to leave the Gotei 13 and become a roaming Shinigami with a personal mission to eliminate all Hollows, especially the one who took his wife's life, in pursuit of revenge.