Early life Born in
Chiba, Chiba prefecture; Japan on November 5, 1985, Tanaka is the second oldest of 5 siblings, all brothers and raised by their single mother. His younger brother Juri is also an actor and signed with Johnny & Associates. Juri along with Tanaka's youngest brother Subaru even appeared alongside Tanaka in the first episode of the TV series
Tokkyu Tanaka 3 Go in which Tanaka played the lead role. His younger brother Hyouga is also an actor, and Tanaka's older brother is named Kazunaru. Before Tanaka was born, his mother thought he would be a girl, so she thought of the name Maria (Saint). But he turned out to be a boy instead, so the Kanji letter of his name '聖' was kept, but its pronunciation was changed to “Kōki” (“Kōki” also means “Saint” in Japanese). Furthermore, when he was little his face was so cute and feminine that he was often mistaken for a girl. Tanaka graduated from
Horikoshi High School, and eventually went to study at
Josai International University, but he quit halfway. He loves animals so much that he originally wanted to become a veterinarian.
Career Tanaka joined
Johnny & Associates in 1998 when he was only 13 years old, he once stated the reason why he applied was “My mother sent the application form behind my back. So I went to the audition without knowing anything at all. She told me it was because my cousin applied too. Therefore, we went to the audition together. But in the end, my cousin failed, while I passed.” He became a member of Jpop idol boy band
KAT-TUN from their debut in 2001 until September 30, 2013, when his contract with Johnny & Associates was terminated due to several contract violations and he left the company. In November the same year he formed his own Indie rock band called
INKT and was the lead vocalist in the band, and they finally released their debut album on November 8, 2014. On September 1, 2017, it was announced on the band's website that INKT has now officially disbanded. After the band's disbandment, Tanaka still continues to release music and perform in live shows as a solo artist. On January 23, 2019, Tanaka released his first solo album
Easter under his own record label 'Project KOKI', followed by a solo national tour in Japan from February 2 to April 6, 2019. On July 31, 2019, Tanaka released his solo single
Round and Round / end of begin and held a one-man solo live tour in August and a band tour in October. He then released a mini album
LOUDER on October 2, 2019. On January 5, 2020, Tanaka started his own official YouTube channel where he uploads original content often featuring him with his younger brother Hyouga. In 2020 Tanaka announced that he would write, direct and star in his own stage show called
OLD Maid-JOKER, the shows were originally scheduled to begin in June 2020 but had to be postponed due to the
COVID-19 pandemic, the shows have since been rescheduled to play from April 21–25, 2021. Since February 22, 2021 Tanaka has started a radio podcast show with his brother Hyouga called
Tanaka Family Raaaaadio which broadcasts shows weekly every Sundays in Japan. As an actor, Tanaka has appeared in a string of Japanese TV series and movies and has won 2 awards for his acting work in
My Boss My Hero. ==Personal life==