Shinjurou Rengoku

Shinjurou is introduced as bitter, abrasive, dismissive, and heavily dependent on alcohol. He belittles the accomplishments of Kyoujurou Rengoku and discourages Senjurou Rengoku from following the same path, creating an emotionally oppressive atmosphere in the Rengoku household.

His behavior grew from despair rather than lifelong indifference. Shinjurou had once trained Kyoujurou personally and fulfilled the responsibilities of a Hashira. Discovering the superiority and historical importance of Sun Breathing shattered his pride in Flame Breathing, while the loss of Ruka Rengoku deepened his decline.

Shinjurou retains a capacity for reflection and affection beneath his hostility. Kyoujurou's final message forces him to confront his behavior, and he eventually breaks down in tears before beginning to change his attitude.

As a former Flame Hashira, Shinjurou was once among the Demon Slayer Corps' most accomplished swordsmen. He mastered Flame Breathing and possessed the physical conditioning, reflexes, strength, and swordsmanship necessary to attain Hashira rank.

His abilities are shown particularly clearly in Kyoujurou Rengoku's Story, where he is still capable of killing dangerous demons despite his deteriorating motivation.

Shinjurou also possesses substantial historical knowledge derived from records left by previous Flame Hashira. He recognizes Tanjiro's hanafuda earrings and knows about Sun Breathing's relationship to the derivative Breathing Styles.

Shinjurou appears in Kyoujurou's memories as a former mentor who has abandoned both training and encouragement. Kyoujurou nevertheless continues studying Flame Breathing independently and eventually succeeds his father as Flame Hashira.

When Tanjiro Kamado visits the Rengoku residence, Shinjurou reacts aggressively to his hanafuda earrings and accuses him of practicing Sun Breathing. Their argument becomes physical before Senjurou intervenes.

After hearing Kyoujurou's final message, Shinjurou begins reconsidering his behavior. He later sends Tanjiro an apology and provides information about Sun Breathing, and during the final campaign he joins Tengen Uzui in guarding the Ubuyashiki heir and Nezuko.

Kyoujurou Rengoku is Shinjurou's elder son and successor as Flame Hashira. Shinjurou initially trains him but later withdraws and dismisses his achievements. Kyoujurou's final message that he should take care of himself breaks through much of Shinjurou's bitterness.

Senjurou Rengoku is Shinjurou's younger son. Senjurou remains in the family home and endures his father's harsh behavior despite continuing to care for him.

Ruka Rengoku is Shinjurou's wife. Her death from illness contributes significantly to his emotional collapse.

Tanjiro Kamado initially provokes Shinjurou's anger because his hanafuda earrings remind him of the Sun Breathing swordsman described in historical records. Shinjurou later apologizes to Tanjiro and helps him understand the connection between Sun Breathing and the other styles.

Tengen Uzui serves alongside Shinjurou during the final campaign. The two former Hashira guard Kiriya Ubuyashiki and Nezuko while the active Corps battles Muzan's forces.

Kiriya Ubuyashiki is one of the people Shinjurou protects during the final battle.