Bolbbalgan4, also known as BOL4 or Blushing Youth, is a South Korean musical act formed by Shofar Music in 2016. They appeared on Superstar K6 in 2014 before signing a contract with their current agency. BOL4 was originally a duo consisting of Ahn Ji-young and Woo Ji-yoon. They debuted with the single "Fight Day" from the mini-album Red Ickle on April 22, 2016. The first syllable of the Korean word sachungi "puberty" is pronounced the same as the Sino-Korean numeral four, and accordingly the group name is sometimes shortened to BOL4.

King Record Co., Ltd. , commonly known as King Records, is a Japanese record company founded in January 1931 as a division of the Japanese publisher Kodansha. It initially began operating as an independent entity in the 1950s. It later became part of the Otowa Group. Today, King Records is one of Japan's largest record companies which is not owned by a multinational entity. The label's headquarters are in Bunkyo, Tokyo.