Yasui Santetsu belonged to the Yasui House of the Four Houses of Go in 1661, but he had a growing inclination towards mathematics and astronomy. Under the alias Shibukawa Harumi, he was engrossed in solving enthralling scientific problems, particularly those related to devising a fresh Japanese calendar. Shibukawa Harumi, the character from the story, was inspired by the real-life astronomer and calendar reformer Shibukawa Harumi, who existed between 1639-1715. During Harumi's era, the Japanese used an outdated lunar-solar Xuan-ming calendar of China that had not undergone any modification for almost 800 years. Harumi took advantage of his accurate astronomical observations and revamped the calendar. By that point, the winter solstice was already delayed for two days.