Composed of Haruomi Hosono, Takashi Matsumoto, Eiichi Ohtaki and Shigeru Suzuki, the band's pioneering sound was regarded as avant-garde to most Japanese at the time.

"[2] When his band Burns needed a bass player, drummer Takashi Matsumoto reached out to Haruomi Hosono, a Rikkyo University student whom he heard was quite skilled.

"[5] However, the relationships between band members deteriorated between the April 1969 recording of their debut album and its September release date, so Apryl Fool decided to break up in October 1969.

[6] In December, Shigeru Suzuki, who already had a reputation as a skilled guitarist in the band Skye, was invited to join after Hosono and Matsumoto heard him improvise over what would become "Juuni Gatsu no Ame no hi".

[8] Matsumoto stated that at the time Happy End started, they were influenced by Moby Grape, Buffalo Springfield, and the Grateful Dead.

[10] It marked an important turning point in Japanese music history, as it sparked what would be known as the "Japanese-language Rock Controversy" (ja:日本語ロック論争, Nihongo Rokku Ronsō).

The success of Happy End's debut album and their second, Kazemachi Roman released a year later, proved the sustainability of Japanese-language rock in Japan.

[10] Although Hosono later described the work with Parks as "productive," the album sessions were tenuous, and the members of Happy End were disenchanted with their vision of America they had anticipated.

Matsumoto became one of the most successful lyricists in the country and Ohtaki worked as a songwriter and solo artist, releasing one of Japan's best-selling and most critically acclaimed albums, A Long Vacation in 1981.

[20] Matsumoto, Hosono and Suzuki opened each day by performing "Natsu Nandesu" and "Hana Ichi Monme", immediately followed by "Haikara Hakuchi" with Motoharu Sano.

[21] The three surviving members of Happy End reunited again on November 5–6, 2021 for a two-day concert, that also featured numerous other artists, at the Nippon Budokan to celebrate Matsumoto's 50th anniversary.

There were bands tied to that latter movement like The Golden Cups and The Spiders, who were active in the Yokohama scene, which was a really interesting music community because it had a huge American influence owing to the navy base in nearby Yokosuka.

"[5] According to music critic Ian Martin, Happy End pioneered a style of songwriting that combined Japanese-language lyrics with Western-influenced folk rock in a one-syllable one-note rhythmic form.

[26] Happy End's music has been cited as one of the origins of modern "J-pop", with each member continuing to contribute to its development after the group's break up.