siinamota (Shiina Mota), popularly known as Powapowa-P (P), was a composer for the Japanese music label GINGA. His real name was Ryo Mizoguchi (Mizoguchi Ryou). He was born in Ishikawa Prefecture on March 9, 1995, with the blood type AB. On July 23rd, 2015, he passed away. Though the reason of death has not been confirmed, the timing of the release of a song and various tweets strongly suggest that it was a suicide.

He was a highly influential vocaloid producer throughout his lifetime, achieving acclaim for his distinctive use of rhythm and arrangement. He also produced CDs for the record label U/M/A/A (Universal Music and Arts).