Short answers, pulled from the story.
J-pop stands for Japanese popular music. The term entered the musical mainstream of Japan in the 1990s, though it was first applied narrowly to Western-style acts in Japan just after radio station J-Wave was established.
Kyu Sakamoto's 1961 song "Ue wo Muite Arukō," released in the United States in 1963 as "Sukiyaki," was the first Japanese song to reach number one in the United States. It spent four weeks at the top of Cash Box and three weeks at the top of Billboard, and received a gold record for selling one million copies.
Hikaru Utada's debut Japanese album First Love, released in March 1999, is the best-selling album in Oricon history with 7.65 million copies sold.
As of 2016, the top five best-selling artists in Japanese Oricon chart history are B'z, Mr. Children, Ayumi Hamasaki, Southern All Stars, and Dreams Come True. Among the five, Hamasaki holds the record for being the only solo artist.
Yellow Magic Orchestra, whose members were Haruomi Hosono, Yukihiro Takahashi, and Ryuichi Sakamoto, pioneered technopop, synthpop, and electro music in Japan. Their 1979 album Solid State Survivor sold two million records worldwide and reached number one on the Oricon charts, and their influence caused Japanese pop music to become increasingly dominated by electronic music. Both YMO and Southern All Stars were later ranked at the top of HMV's list of the top 100 Japanese musicians of all time.
Yoasobi's song "Idol" was the first Japanese song to reach number one on the Billboard Global Excl. U.S. chart, as well as on the Apple Music and YouTube Music charts. This milestone occurred in the 2020s.