Around this time, he became acquaintances with the French critic Michel Tapié who was involved with the Gutai group. Onishi participated in several shows that the Gutai group hosted through this relationship. In 1957, Contemporary World Art, an international exhibition curated by Tapié, featured Onishi's abstract ink paintings. The show focused on Art Informel and was first exhibited at the Bridgestone Museum of Art in Tokyo, and later at the Daimaru Department Store in Osaka. In 1958, he participated in the Osaka International Festival—The International Art of a New Era: Informel and Gutai, first exhibited in Osaka and later toured to Nagasaki, Hiroshima, Tokyo, and Kyoto. In 1959, he appeared in the Fifteen Japanese Contemporary Artists Recommended by Tapié at Gendai Gallery in Tokyo.
