[1] He is the Shihan (Chief Instructor) of the SKA, and to this day holds the rank of 5th dan, which was awarded to him by Gichin Funakoshi.

[1] There, he trained under Shotokan's founder, Gichin Funakoshi, and later became captain of the university's karate club in 1952.

[1] Ohshima's seniors at the club also influenced his development in karate; they included Shigeru Egami, Toshio Kamata-Watanabe, Hiroshi Noguchi, Tadao Okuyama, and Matsuo Shibuya.

[1] It was also during this period that he befriended Mitsusuke Harada, who would go on to become a pioneer of karate in Brazil and the United Kingdom.

[5][6] In 1955, Ohshima travelled from Japan to the United States of America to continue his tertiary studies in economics at the University of Southern California.

[1] It was around this time that Ohshima invited Hidetaka Nishiyama to take charge of his karate students in the US, as he was planning to return to Japan following completion of his US university studies.

[10] The award recognized "the role he has played in the development of karate in the United States and the world over" (p. 63).

[7][16] On May 22, 1994, around one hundred Caltech alumni assembled in the institution's gymnasium to honour Ohshima on the occasion of his retirement.

[17] Apart from being the SKA's Shihan, he holds a similar position in Canada Shotokan Karate and other affiliated organizations.

[20] Ohshima officially retired as Shihan in August, 2018 when, at the age of 88, he appointed his successors in SKA and affiliated organizations.