In 1959, Mukai met Jiro Yoshihara who was the leader of GUTAI group. Mukai’s talent was highly appreciated by Yoshihara, and he became the youngest member of GUTAI in 1961. Mukai’s works are composed of many numbers of various types of symbols that fill the canvases and spaces. Yoshihara praised his works saying, “While they appear cool at first glance, there is a furious energy lurking within them.” His works also gained great admiration of Michel Tapié who originated the Art Informel (informal art) movement. In 1964, Mukai’s works were presented at the “New Japanese Painting and Sculpture” exhibition organized by the Museum of Modern Art (MoMA), New York, which toured the United States until 1967. The curator William S. Lieberman purchased two of his works to be added to the collection of the MoMA. In 1966, Mukai presented his first installation work in Osaka, in which symbols filled the entire interior surface of a jazz cafe called “Check”. In 1969, there was an incident in which Mukai burnt all his works and took a break. Later, in 1990, he restarted producing art works. At the “Gutai: Splendid Playground” exhibition held in 2013 at the Guggenheim Museum, New York, he presented an installation work that covered the surfaces of the elevators and bathrooms of the museum in symbols. During the opening event he appeared in the main performance, in which he collaborated with young people using symbols, and gained recognition. In 2014, Mukai created an installation work “Playing with Symbols: Embellished Amphitheater” at the Hyogo Prefectural Museum of Art, curated by architect Tadao Ando. In addition, his retrospectives were held at the Nariwa Museum, Takahashi City, and the Karuizawa New Art Museum. In the following year he presented Space of Signs Selfie Studio installation work that consists of mirrors covered with symbols at the Palazzo Fortuny (Venice).

In December 2016, he created Sky Space Earth, an installation work of pillars covered with symbols, for the new Louis Vuitton store that opened in Soho, New York, under the curation of architect Peter Mariono. In spring 2017, he will present an installation work, which covers the entire surface of the bathroom of The Warehouse, an art exhibition space in Dallas managed by Howard Rachofsky. For the grand opening of Chanel's Tokyo new building in December 2017, designed by Peter Marino, Mukai covered the whole building with his symbols. Thus, Mukai is further expanding his sphere of creative activities.