Prior to taking his wife's surname, Ichigo's father was originally captain of Squad 10 two decades ago. It is unknown what his relationships are with the other members of the "Shiba", most notably with Kaien Shiba, who bears a strong resemblance to Ichigo. Most of his actions as a Soul Reaper remain unknown, except for the events at Naruki City, where he met the Quincy Masaki Kurosaki while fighting Aizen's hollow White. When Masaki is bitten by White, she undergoes hollowfication before Isshin stopped it by renouncing his Soul Reaper powers and linking his soul to hers to halt the process. This resulted in Isshin remaining in the World of Living as . Having lost Masaki to the elusive Hollow Grand Fisher, Isshin regained his Soul Reaper powers yet concealed it from his family for some time as he killed off the Arrancar that Grand Fisher became while regretting that he did not have his power prior to save Masaki. Isshin eventually reveals himself as a Soul Reaper to Ichigo while aiding him in his fight with Aizen, appearing just as the villain was about to reveal his son's lineage as the offspring of a Soul Reaper and a Quincy. Seventeen months later, after Ichigo regains his Soul Reaper powers and the Wandenreich complete their first invasion of the Soul Society, Isshin appears to Ichigo in his Soul Reaper attire and explains Ichigo's past to him.