Koshi Inaba is a celebrated Japanese singer, songwriter, and multi-instrumentalist, best known as the powerful vocalist and lyricist of B'z, Japan's best-selling music act. He launched a solo career in 1997 with the album Magma, reaching the top of Japanese music charts.

Inaba has collaborated internationally, working with artists like Slash (on the 2009 single "Sahara"), and Steve Vai ("Asian Sky", 1999).

On June 29, 2025, Koshi Inaba performed live with ONE OK ROCK at B'z presents UNITE #02 held at K-Arena Yokohama. Together, they delivered a powerful rendition of ONE OK ROCK's signature song The Beginning, creating an emotional and unforgettable moment that brought together two generations of Japanese rock.

The performance was celebrated as a symbol of mutual respect and artistic connection between Inaba and ONE OK ROCK, marking a rare and historic collaboration on stage.