Infinite F was a sub-unit of the South Korean boy band Infinite. The group consisted of vocalists Sungyeol, L, and Sungjong. The trio's journey began unofficially during an Infinite fan meeting in August 2011, where they covered Orange Caramel's "Bangkok City," which garnered positive reactions. Their official announcement came in early 2014 during the Infinite concert One Great Step Returns, where they performed "Heartthrob," a track that would later be used as the main song for the drama Hi! School-Love On, featuring Sungyeol. The group's first official release, the song "Going Crazy," was included as part of Infinite's second Korean studio album, Season 2. Following this, they released the single album Koi no Sign in Japan in 2014, which debuted at number 6 on the Oricon chart with over 31,000 copies sold. The group also released their Korean debut Azure (2014), with the song "Heartthrob" achieving a good amount of popularity. Azure peaked at number 1 on the Korean charts. Infinite F established themselves firmly in both Japan and Korea, continuing to release successful singles such as "It's You" and "My Girl." The group was active until 2019