Eijuin was a woman who lived during the Azuchi-Momoyama and early Edo periods. She was the eldest daughter of Honda Tadamasa, the head of the Himeji domain. Her mother was Myōkō-in (also known as Kumahime or Kunihime), the second daughter of Matsudaira Nobuyasu. Eijuin was the formal wife of Hori Tadatoshi of the Echigo-Takada domain (also known as the Echigo-Fukushima domain). Later, she became the formal wife of Arima Naozumi of the Hyūga-Nobeoka domain in Kyūshū. Her real name was Kunihime.
In the tenth month of 1605, she was adopted by her great-grandfather – Tokugawa Ieyasu. Kunihime wed Hori Tadatoshi but, in the spring of 1609, Tadatoshi was removed from his position so they separated.
In the eleventh month of 1610, Eijuin re-married to Arima Naozumi. At this time, she received a dowry of 1,100 koku in the northern part of Mino Province. Together with Naozumi, she bore two boys and three girls (Yasuzumi, the wife of Honda Masakatsu, the adopted younger sister of Honda Masakatsu, the wife of Akimoto Tomitomo, and Sumimasa).
Kunihide died in 1649 at the age of fifty-five. She was interred at the Tentoku Temple in Edo.