|Japanese name:||黒崎 一心|
Despite his outrageous guise, however, Isshin can be serious and grim at times. On the date of Masaki's death, Isshin smokes a single cigarette in front of her grave, since she thought it made him look cool (she said it when they were dating). He reflects that it was the first and last time she ever complimented his appearance. He also told Ichigo that he shouldn't blame himself for his mother's death because she gave her life to protect him. In addition, during his confrontation with the arrancar Grand Fisher and the subsequent chat with Kisuke Urahara, he remains completely serious (aside from a short argument between him and Kon about his parenting, and another, albeit short, between him and Urahara after the latter likens him to his son).
Isshin appears to be an associate of Kisuke Urahara and possesses knowledge of Sōsuke Aizen's alliance with the Menos. He mentions in his conversation with Urahara that he encountered arrancar about ten years before the main storyline, though they were nowhere near as complete as Fisher. He also reveals to Kon that he has been aware of Ichigo's shinigami activities and Kon's substitutions since Grand Fisher's first attack. He also notes that he has never called Kon "Ichigo" while Kon is in Ichigo's body and that the traveling charm he gave Ichigo before he went to rescue Rukia was actually for Kon (it's a protection talisman). This shows the sensitivity and propriety that he possesses of his role as Ichigo's father, which is rarely portrayed in the series.
Isshin also shares a relationship with Ryūken Ishida not unlike that of their sons. When Ryūken discovers his son is missing, Isshin pays him a visit and the two chat about their respective styles of parenting. It is then revealed that Ryūken was aware of Isshin's status, and he comments on Isshin's powers. The Bleach Official Animation Book VIBEs states that the two have some prior history together, and that they have been acquaintances for quite some time. It can also be noted they both are doctors, Isshin runs a clinic while Ryūken runs a hospital. There have been hints that the two cooperate on a professional level, with Isshin handling minor cases, and occasionally requesting aid from Ryūken.
Theme song: "Don't Drag Me Down" by Social Distortion
Seiyuu: Morikawa Toshiyuki