Along with Tsuyoshi Domoto (with whom he has no blood-relation), he is a member of the duo KinKi Kids, who holds the Guinness World Records for having the most consecutive No.1 singles since debut and the most consecutive years with a Japanese No.1 single, and is one of the top 20 best-selling artists of all time in Japan.
Born in Ashiya, Hyōgo, Japan, Domoto joined the Japanese talent agency Johnny & Associates at the age of 12 after his sister sent in his application without his knowledge.
From July to September 2018, he starred as Arcite in John Caird's musical Knights’ Tale, which was an adaptation of William Shakespeare's The Two Noble Kinsmen, at Imperial Theatre.
[9] Since 2019, Domoto took over the position of director of another musical DREAM BOYS produced by Johnny & Associates and played by his junior colleagues.
It was believed that idols were unqualified to stand at the most famous and important theatre in Japan, let alone playing the lead at the age of 21.
In 2018, Domoto played the lead in Endless SHOCK and Knights’ Tale from February to March and from July to August respectively at Imperial Theatre, becoming the fourth person in history and the first person in 26 years to play a lead for four months in a year at Imperial Theatre.
From July 1994 to September 1994, Domoto and his bandmate Tsuyoshi appeared in drama Ningen Shikkaku, which had a peak rating of 28.9% on its final episode.
He shifted his focus to musicals after starring in Remote from October to December 2002, where he won the 'best supporting actor' in the 35th Drama Academy Award.
To commemorate the 20th anniversary of KinKi Kids, the sequel of 1997 drama Bokura no Yūki Miman City was broadcast as a special drama Bokura no Yūki Miman City: 2017 in NTV, where Domoto played the same character as before.
On January 11, 2006, he released his first CD album Koichi Domoto「Endless Shock」Original Sound Track, but was not regarded as his solo debut.
Domoto released his first DVD/Blu-ray single INTERACTIONAL/SHOW ME UR MONSTER on June 10, 2015, followed by his fourth solo album Spiral on July 8.
The album also featured a collaboration short movie made by Square Enix, in which Domoto himself and a CG version of him starred together.
Since then, he wrote a great number of songs, mainly devoted to the group, his solo work and musical SHOCK.
In 2002, Domoto wrote the lyrics for and composed KinKi Kids' single Solitude ~Hontou no Sayonara~, which was also the theme song for his drama Remote, under the pen name "K．Dino".
Domoto has also provided songs for other artists from Johnny & Associates, such as NEWS, Hideaki Takizawa, and the musical DREAM BOYS.