Founded by Seishiro Okazaki (1890–1951) in Hawaii. Danzan-ryū jujutsu is of mainly Japanese origin but is most common in the West coast of the United States. The Danzan-ryū syllabus is a blend of both Japanese and non-Japanese elements. Seishiro Okazaki was born in Fukushima Prefecture, Japan in 1890. In 1906, he immigrated to the island of Hawaii. Soon after, he was afflicted with a pulmonary condition which may have been tuberculosis. It was during this time, however, that young Okazaki began studying under Yōshin-ryū jujutsu sensei by the name of Yoshimatsu Tanaka in Hilo, Hawaii. Okazaki intensely pursued his studies under Tanaka and he found after sometime that his respiratory condition had gone into remission. Okazaki felt that the study of martial arts had played a large role in his physical recovery and as a result he decided to dedicate his life to the study and teaching of jujitsu and related disciplines. Later in his life he would adopt the Western first name, Henry.
In 1924, Okazaki returned to Japan and underwent a study of the various schools, or ryū-ha, of the then most popular Jūjutsu styles of Yōshin-ryū, Namba-Shoshin Ryū, Iwaga Ryū, Kosogabe Ryū, Kōdōkan Jūdō, and several others. Later that year when he returned to the Hawaiian Islands, he continued the study of jūjutsu under the various masters who had emigrated from Japan to Hawaii. Incorporating not only traditional jūjutsu, but also Lua, Shōrin-ryū Karate, Eskrima, Boxing, Chin Na and Folk Wrestling, he began to synthesize the most effective aspects of these various styles into an eclectic system which he called Danzan Ryū. Okazaki used this name to honor his Chinese martial arts teacher, Wo Chong. The Chinese name for Hawai'i is T'an Shan. When used in Japanese, these kanji are pronounced Dan Zan. Their literal meaning is "sandalwood mountain".
Okazaki's school was founded in Hawaii. The name Kodenkan may be translated as 'The School of the Ancient Tradition'. Okazaki's method of instruction prescribed that senior students to teach their junior students in the spirit of mutual assistance. Okazaki declared that this method of instruction was the foundational philosophy of the American Judo and Jujitsu Federation (AJJF). Okazaki called this philosophy kokua, which in Hawaiian is defined as to mutually help one another. Okazaki was willing to teach both people of non-Asian extraction and women the arts. This was frowned upon by parts of the Asian community in Hawaii at that time. By all accounts the original classes were grueling and Okazaki taught different courses to different individuals. Around the time of the founding of Kodenkan it took approximately four years to earn a Shodan (Black Belt) ranking. During this time students trained 6–7 days a week.
"Upon completing about a year of study," Okazaki wrote in his Esoteric Principles (contained in the Mokuroku scroll given to his pupils who mastered his system), "I acquired a body of iron" (paraphrased), so he dedicated his life to the study of martial arts and the healing techniques associated with each style he took up. Some among his students carried on his healing traditions. In 1984 third and fourth generation devotees standardized his style of massage from notes by Okazaki's students into the AJJF certification program in Okazaki Restorative Massage; recognized by the American Organization for Bodywork Therapies of Asia (AOBTA) , but also known as Okazaki Long Life, Nikko Restorative Massage)