Johnny's Jr.
When Aiba joined Johnny & Associates, he was a member of temporary Johnny's Jr. units such as M.A.I.N. and B.B.B. with fellow Arashi members Matsumoto and Ninomiya and Johnny's Jr. member Toma Ikuta, and B.A.D. with Ninomiya before the formation of Arashi in 1999 in which Aiba was the fifth and last member to be recruited into Arashi.

Arashi
On September 15, 1999 aboard a cruise ship off the coast of Honolulu, Hawai?i, it was announced that a new Johnny's group named Arashi, the Japanese word for storm, would make their debut on November 3, 1999. Their debut single, "Arashi", was used as the image song for the 8th World Cup of Volleyball hosted by Japan in 1999 and the group served as special supporters for the competition. The single went on to become a major hit, selling 557,430 copies in its first week and almost a million copies by the end of its chart run.

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