Isshin Kurosaki

Isshin Kurosaki, father of three children—Ichigo, Yuzu, and Karin—runs a local clinic called "Kurosaki Clinic." He is energetic throughout the year, especially towards his children, and is particularly overprotective of Yuzu and Karin. Initially, he appeared to have no spiritual awareness, but he was actually a former Soul Reaper, Seigen Suzunami, who served as the captain of the 10th Division of the Gotei 13 about 20 years ago. He was born into a branch family of the noble Shiba clan and was known for his easygoing and optimistic nature even then. He met his wife, Masaki, during a mission in the living world when she, then a high school student, saved him from a dire situation involving a modified Hollow, White, created by Aizen.

Later, to repay her, he went to the living world, where he found that she, a Quincy, was on the verge of becoming a Hollow due to injuries she sustained at that time, putting her life at risk. With the help of Kisuke Urahara, they used a special artificial body to connect his and Masaki's souls with the Hollow inside her, successfully suppressing her Hollowfication. This procedure prevented him from returning to being a Soul Reaper until her death, but he chose to protect her without hesitation. He abandoned his return to the Soul Society without notifying the Gotei 13, thus was treated as missing. Later, using the medical knowledge he acquired during his time at the Spiritual Arts Academy, he opened "Kurosaki Clinic" with Urahara's help, started a life in the living world, and eventually married Masaki, becoming the father of Ichigo and his sisters.

Isshin was an old acquaintance of Ryuuken Ishida, Uryuu's father, knowing each other's true identities since the time he met Masaki, and they remained in contact even after her death.

At the beginning of the Arrancar arc, Isshin returned as a Soul Reaper after 20 years, defeating Grand Fisher and avenging Masaki. In the final stages of the same arc, he joined the battle in Karakura Town, fought evenly against Aizen, but was defeated by Aizen transformed by the Hogyoku. Later, while pursuing Aizen, he advised Ichigo on acquiring the "Final Getsuga Tensho" in the Dangai, and took on the task of stopping the Koryu to buy time for Ichigo to master it.

In the Lost Substitute Shinigami arc, he collaborated with Urahara to help Ichigo regain his Soul Reaper powers. In the novel "The Death Save The Strawberry," he hesitated to send Ichigo back to the battlefield but decided to help Urahara after seeing Ichigo tormented by his powerlessness, reflecting on his inability to save Masaki.

In the Thousand-Year Blood War arc, Isshin was sent back to the living world by Nimaiya Oetsu and shared his past with Ichigo, helping him understand his roots and the nature of his soul. He did not participate in the final battle and did not appear in the final chapter, arriving at the Royal Palace with Ryuuken when Ichigo and Yhwach began their battle, but did not engage in combat.

His Zanpakuto, "Engetsu," has a wide blade and a hilt wrapped with a cord, which he carries tied to his belt. When releasing its power, the hilt's cord and blade are enveloped in flames. He can enlarge the blade's flames by blowing his own blood onto it. He has achieved Bankai, but it is physically taxing and was not used in the series, leaving its abilities unknown. He once mentioned having used the "Final Getsuga Tensho," but the details were never revealed.

Ichigo's Zanpakuto, "Zangetsu," shares similar properties with Engetsu, and based on this Zanpakuto, Urahara created a sword imbued with the spiritual pressure of all captain-class Soul Reapers to restore Ichigo's Soul Reaper powers (from the novel "The Death Save The Strawberry"). The release command for Engetsu is "Burn, Engetsu."