Sabato Kuroi, a founding member and master swordsman of the Ittō-ryū, trained under Anotsu Saburō, grandfather of leader Anotsu Kagehisa. His involvement with the group began during Kagehisa's childhood, playing a role in the school's formation.

Kuroi recited poetry referencing the band Black Sabbath—the direct inspiration for his name, as "Kuroi Sabato" roughly translates to "Black Sabbath." He harbored an obsession with preserving ageless beauty, practicing taxidermy on the heads of women he killed. He mounted the preserved heads of his deceased wife and Rin Asano's mother, O-Toki Asano, upon his shoulders.

As a core Ittō-ryū member, Kuroi participated in the assault on the Mutenichi-ryū dojo. There, he killed Rin's father, Kurose, and beheaded O-Toki. He later developed a fixation on Rin, sending her nightly love letters for two years. This culminated in a meeting where he attempted to coerce her into a suicide pact, intending to add her preserved head to his collection alongside her mother's.

In combat, Kuroi wielded two unnamed katana and two specialized shuriken named "Karasu" or "The Crow." He initially overwhelmed both Rin and Manji during their encounter. However, underestimating Manji's regenerative abilities led to Kuroi's death at his hands, making him the first Ittō-ryū member to perish in the conflict. His shuriken, Karasu, were temporarily claimed by Manji afterward.