Okamoto Seigo entered the dojo of Horikawa Sensei at the age of 38. Training 5 nights per week for many years, Okamoto slowly became the most senior of the students in the dojo as was teaching many classes per week under the guidance of Horikawa Sensei.

Okamoto Seigo was the first of Kodo's students to receive 7th Dan. Okamoto Soshi received the Shihan, or Masters License in 1978. Adhering to Japanese martial tradition, Okamoto founded Daito-ryu Aikijujitsu Roppokai in 1980, the year Kodo sensei died.

In 1985, Okamoto founded the first foreign branch of the Roppokai in Denmark. In 1997, Howard Popkin traveled to Tokyo, Japan to train with Okamoto Sensei and was given permission to form the New York Roppokai.