[2][3] Originally a nine-piece ensemble, former members Kang Ye-seo and Sakamoto Mashiro departed from the group in July 2024.

The group debuted on January 3, 2022, under the co-management of WakeOne and Swing Entertainment with their first extended play (EP) First Impact.

[4] Upon its release, the group received immediate commercial success, selling approximately 400,000 copies and peaking at number 1 on South Korea's Gaon Album Chart.

[12] Kep1er was formed through the Mnet reality survival show Girls Planet 999, which aired from August 6 to October 22, 2021.

The show brought 99 contestants from China, Japan, and South Korea to compete to debut in a multinational girl group.

[20] Kep1er was originally scheduled to debut on December 14, 2021, with pre-orders for their EP First Impact having begun on November 29.

[22] However, it was announced that the group's scheduled debut had been delayed to January 3, 2022, after one of their staff members tested positive for COVID-19.

[28][29] On January 10, Chaehyun was announced as the new co-host for SBS MTV's music program The Show alongside Ateez's Yeosang and Cravity's Minhee.

[31] On February 21, 2022, it was confirmed that Kep1er will participate in the second season of the Mnet reality competition show Queendom, scheduled to premiere in March 2022.

[37] On February 14, 2023, WakeOne and Swing Entertainment announced the dates for Kep1er Japan Concert Tour 2023 'Fly-By', which will be held in Aichi and Hyogo.

[44] On November 22, the group released their third Japanese single Fly-High, with "Grand Prix" as the lead track.

[46] On February 14, WakeOne and Swing Entertainment announced that the group's first Japanese studio album Kep1going would be released on May 8.