Kaishu was a samurai, born Katsu Rintarō, in January 1823, in Edo (present day Tokyo) to a low-ranking retainer of the Tokugawa Shogun.
Naturally curious and fascinated of the world around him, new doors to the outside nations beyond Japan opened to him when he first looked at a map of the Earth and came to discover the words on a Dutch made cannon. As the Tokugawa Shogunate came to its last years in the Bakumatsu, Kaishu was instrumental in the formation of Japan's Navy after the arrival of Commodore Matthew C. Perry, and to shaping the ideals and virtues of the famous Sakamoto Ryoma of the Ishin Shishi, establishing a force based upon skill and ability than the right through birth and caste. These acts quickly led Kaishu to rise in the Shogunate's ranks and lead to the birth of his naval academy.
In January, 1860, Katsu Kaishu commanded the famed Kanrin Maru, on its maiden voyage and made Japan's first authorized trip across the Pacific Ocean. Landing into the bay of San Francisco, Kaishu's image of an equal Japan was further reinforced when he saw and observed the everyday workings of American society. Soon after, Kaishu then quickly had grasped a full understanding of the world outside of Japan, knowing of the rise of colonialism by Western nations and the state of its conquered peoples.
During the year of 1862, as the turbulence of the Bakumatsu was to rise, Kaishu was put under house arrest, had his naval academy immediately closed, and was reduced to base stipends after being caught in the act of hiding enemies of the Shogunate. Under the rule of Tokugawa Iemochi, Kaishu's innovative ways even nearly earned him execution, especially when he brought up the factor that the Shogun should relinquish his power in peace, in order to quell the violent uprisings of the pro sonno-joi imperialist rebels.
In 1866, as the armies of Choshu quickly defeated the Shogunate's forces at every battle, Kaishu was immediately summoned back to his lofty post of Navy Commander under the rule of Tokugawa Yoshinobu, and was dispatched to Hiroshima to settle with the Choshu forces. Though he traveled alone and in peace to settle agreements with the representatives of Choshu, after the success of the mission, Kaishu immediately resigned his post back to his home, knowing of the irreconcilable tensions that could not be settled at the moment.
In the following year of 1867, even as Tokugawa Yoshinobu resigned his post to give back power to the Emperor of Japan, the Satcho army still dealt with those who did not agree with the new imperialist government that was to rise in its stead. In 1868, as the Satcho army was to march onto Edo and directly confront the Shogunate to finally dismantle it by war, Kaishu's help as the advisor and direct retainer to Yoshinobu was needed than ever before. Not wanting the bloody civil war to extend to Edo, in March of 1868, Kaishu sent a letter of peaceful negotiation to Saigo Takamori, stating that the retainers of the Tokugawa were an inseparable part of the new Japanese nation, and that, instead of fighting with one another, those of the new government and the old must cooperate in order to deal with the very real threat of the foreign powers, whose legations in Japan anxiously watched the great revolution which had consumed the Japanese nation for these past fifteen years.
Saigo in return, replied with the set of conditions, that Edo Castle be surrendered to the Satcho army, and they would comply with sparing the Tokugawa retainers, Yoshinobu himself, and the entire city of Edo. On March 14th, a day before the planned attack, both Saigo and Kaishu met in person, and fully accepted peaceful terms to spare the new capitol of Japan.
Though he accompanied Yoshinobu to Shizuoka into exile immediately after, Kaishu returned to Tokyo in 1872 and was one of the many Tokugawa retainers that found work in the Meiji Government, servicing the new Imperial Japanese Navy as its Vice Minister, and followed by promotion to first Minister of the Navy from 1873 until 1878.
Kaishu, as he is known in reality, was widely known as a sensible and honorable person that chose peace and abhorred the the option of violence and war. He is much like, if not, greater than Kenshin, in terms of pacifism and settling things with compliance than confrontation, being famous for having tied his katana and saya tight enough where he was not even able to draw it even if he wanted to, and even as a samurai of the Tokugawa himself during the rebellious and violent days of the Bakumatsu.
As a youth, his curiosity for the outside world, compassionate inspiration and visionary spirit that overlooked the ideas of classes and castes were what lead him to be knowledgeable and understanding.
In the anime, Kaishu is portrayed as an easy going, yet fatherly and stern elderly adult figure. Though he is a pacifist, Kaishu showed bravery even amongst a threat for his life, and reprimanded his apprentice Daigoro to have more courage and spirit amidst an ongoing battle. When his daughter demanded the whereabouts of Daigoro after he had dismissed and kicked him out of his tutelage, he expressed that his household had rules, and told her not to come back if she did leave for him.
Nevertheless, Kaishu is shown to have great duties of responsibility, even at an old age, feeling that as a member of the old generation, he must help clean up the messes of his age in the sake of the young and new generation of tomorrow. While with regret that he could not accompany his friend Saigo to the Satsuma Rebellion and save his life, Kaishu is intuitive and with a persevering mind in the long term, feeling the need that his life must still go on to help the new era that is becoming.
As a retainer and ally of the of Tokugawa, Kaishu still holds his allegiance strongly with them. Though appreciative of the peace and the efforts of the Meiji, he still knows that the Meiji fears the once great and legendary influence of the Tokugawas, and that, despite all atrocities that the Shogunate committed that lead to their collapse, feels the people must come to accept and acknowledge the sacrifice and the man that allowed Edo to be spared from the Bakumatsu's chaos.