Koharu
She is Roman's younger sister, who runs a decorative chopstick shop by day and at night she assists with his brother's heroic capers together with their dog, Sakura. Spoiler It was later on reveled that she was not Roman's sister, she is the last princess of the Tokugawa family whose father is the 13th shogun Iesada Tokugawa, she was adopted by Jirokichi upon the latter's dying wish to avoid a possible scandal of his relationship with her mother, Suzu a traveling performer who died giving birth her. (Source: otaku-streamer forum)