Takahiro Moriuchi, better known as Taka, is the main composer and songwriter of the group. In 2017, Kerrang magazine! awarded him 27th place in its ranking of the "50 Greatest Rock stars in the World". Rock Sound magazine also honored him as one of the"50 most Influential Figures in rock".

Taka was born on April 17, 1988 in the family of famous Japanese performers Masako Mori and Shinichi More. He also has 2 younger brothers. His first group was NEWS, but he left the group because he wanted to focus on his studies. In 2004, he was in the band Chivalry of Music, but only for a short time. In 2005, guitarist Toru Yamashita invited Taka to join One Ok Rock.

The biggest influence on his work was provided by the band Linkin Park, Good Charlotte, Korn, Sum 41, Green Day and Simple Plan. He also cites Chester Bennington of Linkin Park and Kellin Quinn of Sleeping with Sirens as his inspirations for changing styles from pop to rock music.