The death was announced in Japan by the Kanagawa Arts Foundation, where Mr. Ichiyanagi was general artistic director. The statement did not give a cause of death or the specific location.
Mr. Ichiyanagi created an expansive catalogue — more than 200 works including piano solos, percussion interplay, operas and string-and-woodwind pieces — that were performed around the world and celebrated as important contributions to musical frontiers along with contemporaries such as David Tudor, Steve Reich and Mr. Ichiyanagi’s mentor, John Cage.
Mr. Ichiyanagi’s influence also extended to Ono’s artistic vision during their 1956-1962 marriage as she experimented with sound, including a dance piece in the early 1960s in which she used microphones to amplify the breathing of the performers.
Mr. Ichiyanagi could leave critics baffled and disappointed, but he was widely acclaimed for his boundless creativity, particularly his use of randomness in performance and the musical dialogue between Western and Japanese traditions.
“Japan has a long history of adapting the practices of Western culture and assembling [them] into their own,” he told the Los Angeles Times in 2015.
In 1989, Mr. Inchiyanagi formed the Tokyo International Music Ensemble — the New Tradition, an orchestral group that used traditional instruments such the zither-like gaku-biwa and Buddhist ritualistic chants called shomyo. His 1960 composition, “Kaiki [Recurrence] for Koto for John Cage,” combined Japanese instruments, the mouth organ known as sho and the stringed koto, with the harmonica and saxophone.
In a nod to Western influences, he created operatic pieces that included “From the Works of Tadanori Yokoo” in 1969 that featured electronic overtures and tapped into Flower Power spirit of graphic artist Yokoo’s psychedelic images.
Mr. Ichiyanagi also pushed in many other directions. “Music for Piano No. 4” (1968) includes a series of squeaks that one reviewer described as similar to turkey calls. “Another work, Distance” (1961) requires performers to use rods or other devices so they can play their instruments from at least three meters away. “Music for Tinguely” (1963) was made from objects by kinetic sculptor Jean Tinguely.
Mr. Ichiyanagi’s written scores became art objects in themselves, some in the collection of New York’s Museum of Modern Art, with Mr. Ichiyanagi adding his own swirls, loops, geometric patterns and instructions for musicians.
In “Music for Electric Metronome” (1960), he asked each musician to start anywhere in the piece they like and then explore options to improvise for the rest of the piece. In 2016 in Tokyo, he performed his “Piano Concerto No. 6, ‘Zen’ ” a six-part piece with no set order.
“Ichiyanagi’s contributions to the experimental practice and tradition are far reaching and comprehensive,” Nomi Epstein, who composes and researches nontraditional music as a professor at Boston’s Berklee College of Music, wrote in an email to The Washington Post.
“As an innovator in notation (with graphic and text scores), he worked to break down the divide between performer and composer,” she wrote, noting that Mr. Ichiyanagi invited performers to do “much more than interpret a score, but rather make decisions about structure, pitch, density, color and sonic activity.”
Toshi Ichiyanagi was born in Kobe, Japan, on Feb. 4, 1933, and was raised in Tokyo by parents involved in music: a father who played the cello and a mother who was a pianist.
After Japan’s surrender in World War II, his mother helped him secure a job playing piano at an American military base, performing songs from Broadway musicals as well as waltzes by Johann Strauss. The soldiers also gave him a first taste of jazz and its stylistic freedoms.
He won music competitions in Japan and enrolled in 1952 at the University of Minnesota to continue his studies. In the summers, he took classes at Tanglewood in western Massachusetts with composer Aaron Copland.
Mr. Ichiyanagi was accepted in 1954 at the Juilliard School in Manhattan, but he became increasingly disinterested in traditional composition. New York’s underground art world provided an alternative. There, he met Ono, who was studying at Sarah Lawrence College in Bronxville, N.Y. They eloped in 1956 after Ono dropped out of college, angered that her cosmopolitan and wealthy parents disapproved of Mr. Ichiyanagi’s more humble roots.
The couple found inspiration in New York’s Fluxus movement, a loose association of artists, musicians, writers and others that emphasized experimental work and collaboration between creative fields.
Mr. Ichiyanagi said he found musical “release” when he was asked to perform in a three-piano piece created by Stefan Wolpe. Also in the group was Tudor, a celebrated pianist and composer of experimental music. Tudor then introduced Mr. Ichiyanagi to Cage, a leading figure in the Fluxus groups.
It was a lifelong bond. In 1958, Mr. Ichiyanagi began studies as one of Cage’s proteges at the New School for Social Research. Cage also helped Mr. Ichiyanagi land a job as pianist at the dance studio of choreographer Merce Cunningham, and opened doors to meet visual artists including Andy Warhol, Frank Stella and Jasper Johns as well as the futurist R. Buckminster Fuller.
At the time, Mr. Ichiyanagi’s marriage with Ono was fraying. They were living separately. Mr. Ichiyanagi returned to his home country in 1960, inviting Cage and Tudor to perform in Tokyo in a groundbreaking moment for experimental music in Japan.
Ono performed some of her music pieces in conjunction with the Cage concerts, but she was dour. “Who was I,” she was later quoted as saying, “but Toshi’s wife and John Cage’s friend?” They divorced in 1962, and Ono had what was described as a “nervous breakdown” about the time their marriage collapsed. She stayed in Tokyo, marrying film producer Tony Cox who had come to visit her. (Ono subsequently married John Lennon of the Beatles in 1969.)
Mr. Ichiyanagi did not remarry. Complete details on survivors were not immediately available. His awards included top cultural honors from France and Japan.
In 2018, Seattle’s Eye Music ensemble released an album with a 50-minute rendering of Mr. Ichiyanagi’s 1963 “Sapporo,” a piece for up to 15 musicians that has no fixed score and lets performers stop, start and riff at will.
“A proper performance of ‘Sapporo’ has no real beginning or ending,” wrote composer and music journalist Michael Schell in a blog for the classic music station KING in Seattle. “It just starts and stops, emerging gently from its surroundings like a Japanese garden.”