Sokaku told Kodo that he needed to master the techniques of "Aiki" due to his short stature. Sokaku instructed him in mostly the Aiki principles.
Horikawa Kodo's techniques became to be known as "very subtle, effective, and strong.
In 1930 Horikawa Kodo received the certification for Dairi Kyoju (Acting Instructor).
One year later, he received the Hiden Mokuroku (Secret Essence). A short time after that he received the certificate for the Hiden Okugi Mokuroku (Secret Essence of Mysteries) and Hiden Aiki Okugi Mokuroku (Secret Essence of Aiki).
In 1974 he received the Eisei Meijin (Order of Eternal Mastership) which is the highest title in Budo society.