Ay-O (Iijima Takao, 1931–present) is a Japanese artist, who has been associated with Fluxus since its international beginnings in the 1960s.

Probably, the best reference to understand the early years of Ay-O is the autobiographical retrospective book in the references "Ay-O, Over the Rainbow, Ay-O Restrospective 1950-2006." In a nutshell: Ay-O started his career in the Demokrato Artist Association, created by Ei-Q. This association promoted artistic freedom and independence in making art. The influence of these values with Ay-O can be seen in a series of early paintings over which he painted a large X because he thought they were not original enough. Another independent movement was close to Democrato in Japan: Sozo Biiku by the collector Kubo Sadajiro Kubo promoting nurturing freedom when teaching art. Both movements started Fukui Prefecture in Japan and explain the special bound Ay-O developed with the Fukui Prefecture. Sozo Biiku's approach is a challenge of the traditional Japanese Master-Student relationship. As such, like naive art, the movement promotes ways independent to the culturally established ones. Kubo also created the "Small Collector Society" to spread art collection in society.

Ay-O was introduced to George Maciunas by Yoko Ono in 1961 and formally joined Maciunas in Fluxus in 1963. Ay-O was known for his Finger Boxes and for his performance events when he was active in Fluxus. He worked closely with fellow Fluxus artists Maciunas, Emmett Williams, Dick Higgins and Nam June Paik.

Ay-O has established a reputation in the avant gardes of Japan, Europe and the United States. In Japan, he is known as the "Rainbow Man" for his use of colorful, rainbow-striped motifs in his artwork. In its purest form some paintings are simple gradations of the Rainbow with up to 192 gradations.

Ay-O represented Japan at the Venice Biennale in 1966 and at the São Paulo Biennale in 1971. He also built the famed "Tactile Rainbow" at the Osaka World's Fair in 1970. In 1971 true to his Demokato debut he adapted 10 American Naive paintings and created a rainbow version that he called Nashville Skyline. In 1987 he did a series of Rainbow Happenings, with Rainbow Happening #17 being a 300m Rainbow Eiffel Tower project in Paris.