Japanese version was released on April 22, 2015. It peaked at number 19 in South Korea and number eight in Japan. The group's first album as an eight-member group, their fifth Korean studio album Lion Heart, was released on August 19, 2015. The album reached number one in South Korea, and at number 11 in Japan. The album sold over 145,000 copies in 2015. It produced three singles; the lead single "Party" reached number one on the Gaon Digital Chart, and number ten on the Japan Hot 100. Following the release of "Party", Girls' Generation appeared on the Billboard Social 50 at number 44 on August 1, 2015. The following week, the group's position on the chart rose to number 22. The follow-up singles "Lion Heart" and "You Think" were made available in conjunction with the release of the album. They charted at numbers four and 30 on the Gaon Digital Chart, respectively. To promote the album, the group starred in a South Korean reality television program titled Channel Girls' Generation. They embarked on Girls' Generation's Phantasia, a concert tour which started on November 21, 2015, in Seoul. With this achievement, Girls' Generation became the first South Korean girl group to hold a fourth concert tour. The group also concurrently embarked on their 4th Japan Tour, which commenced on December 12, 2015, at Nagoya. The Gaon Music Chart announced that Girls' Generation was the most successful girl group of South Korea in 2015. In August 2016, to commemorate the group's ninth anniversary, S.M. Entertainment released a single titled "Sailing (0805)". The lyrics were written by member Sooyoung, highlighting the relationship between the group and their fans. In July 2017, Girls' Generation announced the release of their sixth Korean-language studio album to commemorate the group's tenth anniversary. The album, titled Holiday Night, was released on August 7, 2017. It debuted atop the Billboard World Albums chart, and peaked at number two on the Gaon Album Chart. The album surpassed The Boys as Girls' Generation's fastest-selling Korean-language album in the first week, and sold over 167,000 copies by the end of 2017. In October 2017, Tiffany, Sooyoung, and Seohyun left SM Entertainment on the condition that the group not disband. With the group on an extended hiatus, all members primarily focused on their solo careers. Girls' Generation reunited in September 2021 with an appearance on variety show You Quiz on the Block,