Ichigo’s family is an unusual one, even by shonen standards, but his family tree explains how he became so powerful.
Bleach is one of many shonen action anime where the protagonist’s lineage provides substantial insight into not just their heritage, but the story’s broader lore and even its combat system in some cases. In Bleach‘s case, protagonist Kurosaki Ichigo has inherited practically everything this world has to offer, though he didn’t know it at first.
Ichigo once thought himself a relatively normal boy who can see ghosts and Hollows, but his spiritual gifts come from both sides of the family, with his father Isshin and his late mother Masaki each contributing to their son’s spiritual growth. Ichigo’s family tree is even larger than he once imagined, and it nearly included the Ishida family as well.
Ichigo’s Soul Reaper Ancestry From Isshin
Ichigo grew up with both of his parents but during the main events of Bleach, only his widower father remained — and Isshin has more than a few secrets to share with his son. Isshin is a Soul Reaper himself, something not even Bleach fans knew until he donned his old robes and slew the Arrancar Grand Fisher one night. Isshin’s Soul Reaper status is what helped Ichigo become one when Rukia lent him her powers at the story’s beginning; he also trained his son to ultimately defeat Aizen Sosuke, from one Soul Reaper to another.
But Isshin is no ordinary Soul Reaper turned family man. He was born into the Shiba family, a minor noble clan in the Soul Society, and once served in Squad 10 as Captain Shiba Isshin. This is most relevant to Ichigo because it means the siblings Kukaku, Ganju and most of all, the late Shiba Kaien are all Ichigo’s family. They are specifically his cousins, which explains why the late Kaien physically resembled Ichigo in flashbacks.
It also explains why both Ichigo and Kaien both subscribe to the concept of an intangible “heart” that links two people, a phenomenon that helped give Orihime hope that Ichigo would rescue her in Las Noches. On a more amusing note, this family connection might explain why Kukaku and Ganju both share Ichigo’s fierce temper, including the latter two clashing repeatedly in the “Soul Society” arc. It’s just how this family functions.
Ichigo’s Quincy Ancestry From Masaki
Ichigo’s maternal lineage is even more impactful in the story of Bleach, and Isshin didn’t explain all this to his son until partway through the “Thousand-Year Blood War” arc. The late Kurosaki Masaki was once a pure-blooded Quincy, an Echt Quincy, and notably, she was once arranged to marry Ishida Ryuken to keep the shrinking pool of pure-blood Quincy alive. If that had happened, Ichigo’s friendly rival Ishida Uryu might never have been born, and Ichigo would have been a pure Quincy from the very start. Instead, the tsundere Ishida Ryuken married Kanae and had Uryu with her. In spirit, Ichigo and Uryu are almost family.
What actually happened is that Masaki almost died fighting an artificial Hollow named White, and only the heroic actions of Captain Shiba, Urahara Kisuke and Ryuken himself saved her life. With Kisuke’s aid, Isshin gave up his powers to control the Hollow poisoning Masaki from the inside, and years later, Isshin and a fully-recovered Masaki married. When Masaki became pregnant with her first child, Ichigo, her Quincy blood and White alike were passed on to the child, and Ichigo was born as a Quincy without even knowing it. This is why the Quincy king, Yhwach, once called Ichigo “my son lost in the darkness,” and it’s also why Ichigo can instinctively use the Blut Vene Quincy technique in battle.
Masaki is the reason Ichigo has both an Inner Hollow and Zangetsu inside him. The Inner Hollow is in fact White given a new form, representing Ichigo’s most feral instincts, while Zangetsu is a modified form of Yhwach himself, hence their physical resemblance. It initially appeared that Zangetsu was Ichigo’s zanpakuto spirit; in reality, the Inner Hollow was Ichigo’s true zanpakuto, and Ichigo later bade goodbye to Zangetsu.
It turns out the Quincy Zangetsu had wanted to prevent Ichigo from becoming a Soul Reaper and being exposed to so much harm and danger, but this protective spirit was ultimately banished. In a way, Zangetsu was like the last remnants of Masaki’s protective maternal instincts, but in the end he chose to help Ichigo after all, taking pride in the boy’s accomplishments.