Nezu Jinpachi leads a pirate group on Lake Biwa and forms a sworn brotherhood with Jūzō Kakei during his travels. He possesses a free-spirited personality and dislikes being tied down, with a strong fondness for sake, women, and his ship.

He first appears when rescuing Saizō Kirigakure and others at Jūzō's request. On his ship, he openly admires women, mistaking Yuri for one and later rejecting Isanami due to her small chest size. Jinpachi offers the group shelter if they can drink all his sake barrels, resulting in everyone except Saizō and Jūzō falling asleep on the deck.

After a conversation with Yukimura Sanada, he warms to him and covers him with a jacket against the cold. He then travels to Ueda with Veronica to join the Braves, motivated by Jūzō's promise of a "gorgeous buxom blonde," later revealed as Anastasia. Despite her exposure as a traitor, Jinpachi remains and learns of Isanami's true nature.

While fishing with Veronica the next day, he is interrupted by Anastasia, who attacks to kill the Braves. Rather than anger, he shows enthusiasm to fight and understand her. During their confrontation, he perceives her as a confused woman with a melting icy facade, though she rebukes this and freezes him. Using his lightning manipulation, he breaks free and electrocutes her unconscious. Due to his interest, he spares her life.

After she wakes and expresses distress over fighting for a fake heirloom and her traitor status, Jinpachi suggests she start anew and embrace a free spirit lifestyle. She accepts, and they become traveling partners, observing Ueda Castle from a distance instead of rejoining the Braves.

Jinpachi demonstrates significant combat abilities, including lightning manipulation and considerable physical strength, such as blocking a blow from Miyoshi Seikai Nyudo with one hand and defeating him with a lightning bolt. He has a black panther named Veronica as a companion.