Shinjuro Rengoku

Shinjuro is a muscular, light-skinned man with bushy black brows and bright orange eyes that redden toward the pupils and slant for a harsh appearance. His wild orange hair flares out around his face, reddens at the tips, and is loosely tied back. He resembled Kyojuro closely enough that his older son was, on two occasions, mistaken for him. Quick to anger and abusive, particularly when the Corps or Kyojuro are mentioned, he is an alcoholic whose vilest behavior comes from drinking. A deep sense of inferiority grips him after reading the old Flame Hashira chronicles, which call Sun Breathing the first and finest of all styles.

Shinjuro wed Ruka and brought up two sons, schooling both in swordsmanship until his wife sickened and died and he learned of Sun Breathing's supremacy, after which he gave up teaching and took to drink. He once came close to killing a demon called Hairo but failed to behead it, mourning his wife as he did; he later shredded the family's inherited Flame Hashira chronicle and turned uncooperative with the Corps before quietly stepping down. Years before, he had rescued the young Obanai from that very serpent creature.

Within the dream Kyojuro endures aboard the train, Shinjuro dismisses his son's promotion as worthless. When Tanjiro later visits, Shinjuro notices his hanafuda earrings, identifies him as a Sun Breathing user, and attacks him before being restrained. Sober and remorseful, he writes Tanjiro a letter of apology, praising his sons and the boy's growth, and afterward joins Tengen Uzui in guarding Kiriya and the Ubuyashiki family.

As the former Flame Hashira, Shinjuro was a master of Flame Breathing and a formidable swordsman, shown when he uses the First Form, Unknowing Fire, to rescue a woman and her child from a demon. Even after years of decay, his skill remains such that the untrained Tanjiro stands no chance against him in their brief exchange. His disenchantment with Flame Breathing, however, drove him to neglect both his craft and his sons.