SOLDIER-K (real name: Keitaro Oishi), born March 24, 1985, is a Japanese hip-hop MC from Kitanagoya City, Aichi Prefecture. He began his career in 2011 as part of the duo SOLDIER-K & CHIP. The group gained early recognition with a performance at Japan’s largest hip-hop event, MONSTER VIBES, in 2013. In 2014, they released the CD album UN FINISH nationwide. By 2017, SOLDIER-K was appearing at local festivals like the Kitanagoya City Music Festival. In 2019, the duo released their second album A LIFE, followed by a successful solo live show at Nagoya's Lion Theater. That same year, they performed at the RINKU BEACH FES. In 2022, after over a decade of collaboration, SOLDIER-K & CHIP officially disbanded. SOLDIER-K then pursued a solo career, releasing digital singles including ”PLAYAZ NIGHT feat. ARK TALK BOX" and "INDEPENDENT" in 2023. He continued his live appearances in 2024 at the Kitanagoya Summer Peace Festival. On June 5, 2025, he released the digital single "4ever U&I (feat. Rion)", showcasing a more melodic and emotional direction in his solo work.