Seiji Isobe began his karate career in the Shotokan style of karate as a teenager in his home prefecture of Fukui in northern Japan. After achieving his Shodan in Shotokan, Isobe followed his instinct and embarked on a lifelong pursuit of Kyokushin.

In 1968, Isobe met Sosai and requested the opportunity to open a Kyokushin school to which Sosai agreed. Isobe returned home and established the Fukui Branch. Returning to train at Honbu as an Uchi Deshi in the early 70's, Isobe Shihan became a loyal and trusted instructor at Honbu Dojo for several years, fighting in the 1st, 2nd and 3rd All Japan Open Karate Tournaments while serving his apprenticeship.

Aside from Shihan Isobe's daily physical training at Honbu, a close personal connection with Oyama ensued as Mas Oyama appointed Isobe personal chauffeur, to which he served for nearly 2 years. In 1972, Sosai decided to open a Branch in South America and selected Shihan Isobe to launch the project, "You go to Brazil 1 year to teach", Sosai ordered, to which Isobe replied, "Osu" and he has made Sao Paolo his home ever since.

During the last 3 decades, Shihan Isobe has personally grown IKO South America into one of the largest organizations outside of Japan, governing 100 schools in 6 countries and representing thousands of Kyokushin practitioners on the continent, including his most famous student, Kyokushin World Champion, Francisco Filho.

Shihan Isobe was appointed to the International Committee soon after Sosai's passing and he continues to commit himself and his unique insight to Kancho Matsui and the Kyokushinkaikan. In the last few years, Isobe Shihan has accomplished several Kyokushin milestones, including holding the first Mini World Championship in 1994 in Brazil, launching the Americas Cup events in the USA, bringing the first non-Japanese World Championship title to Brazil in 1999 and most recently, producing the prestigious "Copa do Mundo 2002" - World Cup Team Championship and taking his Brazil Team to yet another world victory.