Genzaburo Inoue, whose name combines the characters for "source" (源 - gen), "three" (三 - sabu/zabu), and "son" (郎 - rou), with the surname "Inoue" meaning "above the well" (井上), serves as captain of the Shinsengumi's Sixth Division. Hailing from Edo, he shares a history of swordplay training with Isami Kondou and Toshizou Hijikata, reflecting their shared village roots and establishing a foundation of significant trust and close connection. His kind and amiable demeanor is particularly evident during his first interaction with Chizuru Yukimura when she awakens at headquarters. Captains close to him use the familiar nickname "Gen-san."

He frequently joins core Shinsengumi members on missions, demonstrating competent combat abilities. Inoue often assumes a supportive role, delivering important news to others and providing reassurance to Chizuru during distress. His loyalty to the Shinsengumi remains unwavering and deeply heartfelt.

A significant event sees him accompany Chizuru to seek reinforcements. Discovering betrayal by the Bakufu forces, he maintains composure and guides Chizuru to flee into a forest. There, they encounter former Bakufu loyalists who have switched allegiances. These individuals kill him as he repeatedly urges Chizuru to escape. His death serves as a catalyst for Chizuru, triggering her to draw her sword for the first time in response to his killing.

In later prequel story arcs, his role includes tending to a younger Ryuunosuke, addressing injuries and providing food. He regularly attends group gatherings in the common room, typically observing rather than actively engaging, but offers quiet support to Hijikata, acknowledging the weight of leadership and assuring him he doesn't bear burdens alone. During the plot to assassinate Serizawa, he remains stationed at headquarters alongside Sanosuke Harada for surveillance and intervenes to prevent Ryuunosuke from entering the conflict zone.

Regarding film adaptations, his involvement generally follows the anime series' storyline. Visual depictions present him as slightly younger and less overtly amiable. Key differences include the absence of his role greeting Chizuru upon her awakening and apologizing for her restraints. His death scene is rendered with less dramatic emphasis. While Hijikata later expresses regret for not saving him in time, scenes depicting the burial of his body are omitted.