Katsura Kogorō was born Wada Kogorō in Chōshū's Hagi castletown. Adopted into the Katsura family at seven after his adoptive father's death, this adoption secured his samurai status despite reducing the family stipend. It enabled his education at the Meirinkan domain school and later Yoshida Shōin's Shōka Sonjuku academy, where he embraced Imperial loyalism. Influenced by his physician father's Dutch learning and Western sciences, witnessing Commodore Perry's "black ships" in 1853 solidified his interest in modernization, coastal defense, and shipbuilding.

Katsura exhibits a serious, rational, and cautious nature, methodically analyzing situations. He demonstrates deep loyalty to comrades like childhood friend Takasugi Shinsaku and mentors such as Yoshida Shōin. His appearance features medium-length dark hair, square-rimmed black glasses, and attire typically including a teal jacket over a red undershirt. Alternative narratives depict a gentle, scholarly presence, noting he was sometimes mistaken for a girl in his youth and carries a mascot named "Fundossy."

Historically and fictionally, Katsura played pivotal Bakumatsu roles. As a Chōshū diplomat in Kyoto, he facilitated the crucial Satchō Alliance between Chōshū and Satsuma, mediated by Sakamoto Ryōma. He narrowly escaped capture during the 1864 Ikedaya incident, allegedly aided by his geisha lover Ikumatsu (later his wife), hiding under Nijō Bridge before fleeing Kyoto. During the Kinmon incident, Chōshū forces under his indirect command failed to seize the Emperor, leading to Kyoto's destruction and his adoption of the alias Niibori Matsusuke.

In the *Bakumatsu* anime, Katsura and Takasugi are transported to an alternate universe where the Tokugawa shogunate endures. He observes anomalies like the rebuilt Susanoo Castle and encounters his corrupted mentor, Mugensai the Second (Shoin), who seeks the Chronometer to repair spacetime rifts. Katsura prioritizes preventing Mugensai from obtaining the device, questioning the morality of correcting time after witnessing Takasugi's potential death. His investigations into ghost lights linked to the Chronometer showcase his analytical approach, such as debunking a village's "tiger spirit" myth as displaced Susanoo soldiers.

In *Bakumatsu Rock*, Katsura is reimagined as a musician and inventor passionate about rock music. He collects scores and creates devices like speakers, amplifiers, and the "Samurai Radar." Tasked with finding his missing mentor Shōin, he forms the band Ultra Souls. He uses his "Peace Soul" power, activated by drumming, to counter the shogunate's mind-controlling "Heaven's Song." Despite clumsiness in daily chores, he invents tools like "Shocking Balls" and "Inversion Generators," relying on intellect over physical strength.

In *Rurouni Kenshin*, Katsura leads the Chōshū Ishin Shishi strategically. He recruits the young assassin Himura Kenshin after witnessing his swordsmanship. Katsura expresses guilt over exploiting Kenshin's skills, inadvertently causing the death of Kenshin's lover, Yukishiro Tomoe. A master of Shintō Munen-ryū swordsmanship, he renounces drawing his sword to avoid becoming a murderer, symbolizing the Bakumatsu's ideals as a "mikoshi." As a Meiji statesman, he drafts the Five Charter Oath and advocates merit-based governance, resigning in protest against military expansions like the Taiwan Expedition. He dies in 1877 during the Satsuma Rebellion.

Across narratives, Katsura's relationships are central. His bond with Takasugi blends camaraderie and ideological synergy, while his marriage to Ikumatsu underscores reliance on her during crises. He mentors figures like Kenshin and Sakamoto Ryōma, balancing tactical ruthlessness with introspection about revolution's costs. His arcs highlight tensions between idealism and pragmatism in political alliances, musical rebellion, and protecting loved ones from altered history's consequences.