Daigo Oishi was born on July 15, 1950, in Yamanashi Prefecture. While in high school, he read “World Fighting Travels” written by Masutatsu Oyama and became deeply devoted to Kyokushin Karate. In March 1969, he entered the Kyokushin Kaikan Honbu (headquarters) dojo and served as an uchi-deshi (live-in student) for five years.
In 1971, at the young age of 21, he competed in the 3rd All Japan Open Karate Championship. Showcasing brilliant kicking techniques such as high roundhouse kicks and spinning kicks, he drew enthusiastic applause from the audience and placed 3rd.
Later, despite competing with injuries, he participated in the 6th All Japan Karate Championship in 1974, where he achieved a remarkable record of four consecutive ippon victories and placed 6th. In 1975, at the historic 1st World Open Karate Championship, he represented Japan and placed 4th.
In 1976, under the directive of Masutatsu Oyama, he was appointed Branch Chief of the Kyokushin Yamanashi branch, and in 1977 he also took on the role of Shizuoka Branch Chief. Since then, he has dedicated himself to the spread and development of Kyokushin Karate, always leading training from the front, sweating alongside his students, and embodying the principle of leading by example as a lifelong active karate practitioner.
His passion extends not only throughout Japan but across the world. Many overseas branch leaders travel to Japan specifically to receive instruction from Kancho (Grand Master) Daigo Oishi.
In 1998, he successfully completed the 70-man kumite.
On January 23, 2003, he received the Social and Cultural Merit Award from the Japan Cultural Promotion Society.
In November 2012, he left the All Japan Kyokushin Federation and, together with Grand Master Kazuyuki Hasegawa, established the International Karate Organization Kyokushin Kaikan World So-Kyokushin, where he serves as Vice Representative.